It's possible to draw one, not the other or just draw them in the wrong order. As we'd only be running 4 of our actual card draw spell it's feasible that some games you'd just never see it.
once a mine effect is on the field you get persistent card draw while digging through your deck and taking extra turns. Every turn taken draws you into more additional gas.
his means many situations will arise where you are taking turns blind, drawing only a single card at a time and hoping that the top card of your deck is an ancestral vision otherwise you lose. Frankly this is the worst aspect of running the As Foretold engine. You are completely reliant on topdecking an ancestral vision and have no other means of card velocity apart from a couple of cantrips.
3) dictate can be flashed in, getting around various forms of interaction such as discard.
Conversely, if your opponent casts an inquisition of kozilek and you're holding either a vision or a foretold (waiting for the other half and casting your interaction in the early turns) your draw engine is gonna get wrecked.
4) you're incentivised to wait on casting as foretold because it does literally nothing by itself.
To be honest, there's no good reason to drop dictate from the deck. Running as foretold *instead* is just bad deckbuilding.