You'd probably be okay with the big Eldrazi and even the bomb 6-drops, as long as you keep their enablers in check. Like Grave Titan isn't unfair if it comes out through natural land drops on turn 6-8, and is even probably fine if you burn some resources to play it Turn 4 off a Diabolic Servitude, Dark Ritual or Worn Powerstone, just be careful with effects that outright disregard normal Mana limits.
I won't speak for LayShade, but when I talk about tuning Mana curves, I'm not as worried about the mean as the skew - I want more spells that can be cast/cycled/suspended/evoked at 2 Mana than 3, more at 3 than 4, and more at 4 than 5, with as few as possible over that.
Then, the harder part is tweaking & making sure that same curve is present and appropriate within my archetypes.
The easiest way to test is just to do some drafts - actual or simulated - and see what cards your decks want, and what kinds of cards they flood out with.
Some examples I waste a lot of time with:
-4 drops: These slots are insanely competitive; it's easy to overload on any of them, but a lot of the time, a good card needs to be replaced with a worse one at a lower cost, or for a different style of deck
-Aggro high-drops: Most aggressive decks want one 5 Mana spell at most. No need to dedicate more than 1-2 EDIT:Aggro 5-drop slots/color. Cards over 5 Mana that want to be aggressive need to be handled deliberately
-"Cheat" targets: There's a balancing act to have enough uncastably expensive fatties to reward your ramp/reanimate/etc drafters, but not enough to weigh down other players' decks
-1 drops: Almost every one is a low-impact card that transfers badly to other archetypes. But without maintaining enough to keep aggro healthy, cube turns into a draw-based mid-range slugfest.
Edit: All these are super subjective, and vary a lot by your goal. If you want to play up tribal synergies, Millstone strategies, etc., you'll probably want more tribal-based aggro, and more expensive/less impactful ramp and reanimation targets
Edit2: ^Thanks for the callout! But as a quick disclaimer, I haven't gotten around to sorting my main 540 on cubetutor, so the analysis results are a little funky
Checked in on the cube again, and it looks like it's getting structured well.
Just keep in mind that expanding our cube with "Top 360" sorts of cards is going to turn the weird archetype additions into blanks - cards like Doorkeeper/Doomed Dissenter/Wolf-Skull Shaman/Waste Not/Wort, the Broodmother could have homes somewhere, but it's not in a world with turn 2 Grave Titan/Wurmcoil Engine/Ulamog, the Infinite Gyre
I'd keep an eye on these cards, which I think could corner out your Tribal/Mill/etc plans:
Balance, Armageddon, Mana Drain, Jace, the Mind Sculptor, Reanimate, Exhume, Recurring Nightmare, Channel, Rofellos and the Swords
I would hesitate to add Mill, Infect or Storm cards that don't win the game on their own or contribute to a more general strategy.
Those are almost always terrible - both for the decks trying to build around them, and for the other players who would otherwise see more usable cards in draft
Edit: Likewise for cards with other parasitic mechanics like Lys Alana Huntmaster or Darksteel Forge that only do anything in one specific deck. Thief of Sanity, Imperious Perfect or Bosh, Iron Golem are examples of thematic cards that work in multiple decks while supporting a specific Mill / Tribal / Artifact plan - they have an archetypes where they do a lot, but they can also be jammed in other decks and do something. The less all-in a strategy is, the better it is for a draft environment
I would skip the common, cycling and maybe tri-colored lands. What your cube looks like now - and what it sounds like with things like Sol Ring coming in - is a real power gap between cards.
That's normal to an extent - in a vacuum Jace, the Mind Sculptor or Wurmcoil Engine and Jackal Pup or Pestermite aren't even close to the same power levels - but they're normalized because those bad cards are part of combos or archetypes where they contribute something important to the game plan.
Right now, your list has a lot of cards that aren't good enough to make retail draft decks, and that don't really have decks for them. Supporting aggro at 360, I want a minimum 5 attacking 1-drops in aggressive colors and at least 10 attacking 2-drops per color. My highest priorities would be shifting the curve down to center around 1-3 mana slots, getting the downright bad cards out ASAP, and then evening out the guilds - I'd give 2 cards per color pair to start, and adjust by taste afterward.
Shocks and checklands are a solid mana base. With the exceptions of ONS/KTK/ZEN fetches and Alpha-Beta duals, you'll get declining benefits from land slots once you have those full cycles, so I probably wouldn't touch lands after that until your colors themselves are better balanced
Opened a tab with your list last night and came here to say the same thing as LeyShade about CMCs.
Most decks you draft will probably be best with more 2-mana spells than 3-mana spells, and more 3-mana spells than 4-mana spells and so on, and the composition of your cube should support that.
There are a lot of cards bunched up at the higher mana costs. As you refine, that's one of the first things to pare down. It will make more cards playable and will make mana screw less of an issue
The next step would be refining the types of decks you support, whether you want to encourage prolonged mid-range slugfests, all-in janky combos, frequent aggro mirrors, tempo v. control fites, etc.
Using cards from your collection is a lot harder than selecting singles. I'd suggest working out a cube list you want within budget before buying anything.
That might sound expensive, but you can make an interesting cube environment with commons, uncommons and bulk rares, where buying bulk would run around $50 for the whole thing.
I won't speak for LayShade, but when I talk about tuning Mana curves, I'm not as worried about the mean as the skew - I want more spells that can be cast/cycled/suspended/evoked at 2 Mana than 3, more at 3 than 4, and more at 4 than 5, with as few as possible over that.
Then, the harder part is tweaking & making sure that same curve is present and appropriate within my archetypes.
The easiest way to test is just to do some drafts - actual or simulated - and see what cards your decks want, and what kinds of cards they flood out with.
Some examples I waste a lot of time with:
-4 drops: These slots are insanely competitive; it's easy to overload on any of them, but a lot of the time, a good card needs to be replaced with a worse one at a lower cost, or for a different style of deck
-Aggro high-drops: Most aggressive decks want one 5 Mana spell at most. No need to dedicate more than 1-2 EDIT:Aggro 5-drop slots/color. Cards over 5 Mana that want to be aggressive need to be handled deliberately
-"Cheat" targets: There's a balancing act to have enough uncastably expensive fatties to reward your ramp/reanimate/etc drafters, but not enough to weigh down other players' decks
-1 drops: Almost every one is a low-impact card that transfers badly to other archetypes. But without maintaining enough to keep aggro healthy, cube turns into a draw-based mid-range slugfest.
Edit: All these are super subjective, and vary a lot by your goal. If you want to play up tribal synergies, Millstone strategies, etc., you'll probably want more tribal-based aggro, and more expensive/less impactful ramp and reanimation targets
Edit2: ^Thanks for the callout! But as a quick disclaimer, I haven't gotten around to sorting my main 540 on cubetutor, so the analysis results are a little funky
Just keep in mind that expanding our cube with "Top 360" sorts of cards is going to turn the weird archetype additions into blanks - cards like Doorkeeper/Doomed Dissenter/Wolf-Skull Shaman/Waste Not/Wort, the Broodmother could have homes somewhere, but it's not in a world with turn 2 Grave Titan/Wurmcoil Engine/Ulamog, the Infinite Gyre
I'd keep an eye on these cards, which I think could corner out your Tribal/Mill/etc plans:
Balance, Armageddon, Mana Drain, Jace, the Mind Sculptor, Reanimate, Exhume, Recurring Nightmare, Channel, Rofellos and the Swords
Those are almost always terrible - both for the decks trying to build around them, and for the other players who would otherwise see more usable cards in draft
Edit: Likewise for cards with other parasitic mechanics like Lys Alana Huntmaster or Darksteel Forge that only do anything in one specific deck. Thief of Sanity, Imperious Perfect or Bosh, Iron Golem are examples of thematic cards that work in multiple decks while supporting a specific Mill / Tribal / Artifact plan - they have an archetypes where they do a lot, but they can also be jammed in other decks and do something. The less all-in a strategy is, the better it is for a draft environment
That's normal to an extent - in a vacuum Jace, the Mind Sculptor or Wurmcoil Engine and Jackal Pup or Pestermite aren't even close to the same power levels - but they're normalized because those bad cards are part of combos or archetypes where they contribute something important to the game plan.
Right now, your list has a lot of cards that aren't good enough to make retail draft decks, and that don't really have decks for them. Supporting aggro at 360, I want a minimum 5 attacking 1-drops in aggressive colors and at least 10 attacking 2-drops per color. My highest priorities would be shifting the curve down to center around 1-3 mana slots, getting the downright bad cards out ASAP, and then evening out the guilds - I'd give 2 cards per color pair to start, and adjust by taste afterward.
Shocks and checklands are a solid mana base. With the exceptions of ONS/KTK/ZEN fetches and Alpha-Beta duals, you'll get declining benefits from land slots once you have those full cycles, so I probably wouldn't touch lands after that until your colors themselves are better balanced
Most decks you draft will probably be best with more 2-mana spells than 3-mana spells, and more 3-mana spells than 4-mana spells and so on, and the composition of your cube should support that.
There are a lot of cards bunched up at the higher mana costs. As you refine, that's one of the first things to pare down. It will make more cards playable and will make mana screw less of an issue
The next step would be refining the types of decks you support, whether you want to encourage prolonged mid-range slugfests, all-in janky combos, frequent aggro mirrors, tempo v. control fites, etc.
That might sound expensive, but you can make an interesting cube environment with commons, uncommons and bulk rares, where buying bulk would run around $50 for the whole thing.