The fetch manabase is for Dryad Arbor, Groundswell and Become Immense.
I would personally cut BI entirely, it's too often a dead card or a tad too expensive to keep a protecting spell up. The loss of Probe hurt bad. A 1-of I can get behind at most. With Scale Up, the deck doesn't need BI as much, my guess is the new spell increases the clock high enough so the deck doesn't need the flashy spells anymore.
Bauble and other cantrips always feel bad in the deck when I play them, so I agree with your friend.
A manabase with Sanctum and the new Waterlogged Grove is tempting.
Your list seems to lack some removal spells to make a bunch of MUs easier game 1. Without the London Mull Rule, I'd say it's better to be a bit interactive in the maindeck. Humans & UR Phoenix are enough to warrant some Dismembers in the main deck, UW control on top of it makes me want to add Spellskite over counterspells. the horror can also turn into a 6/4 and win through normal damage.
Hard to predict what Modern's gonna be with MH1 though. Just guesses.
1
Is it because Instant > sorcery?
Opt, instant speed, scry 1 and maybe blind draw
Sleight of hand, sorcery, draw the best of two, the other one ends up at the bottom of your library.
I tend to lean toward Sleight of hand but recent winning decklists run 4 Opt and 0 Sleight of hand.
What am I missing here?