What's the EV of "you may play the top of your deck" in terms of card draw?
With no qualifiers (
Future Sight) you'd expect to brick a second land after ~5 cards? So you get 4 cards on average? Ofc this assumes you can cast all spells which obviously won't be the case especially early-game, making these effects worse early.
With casting only, first land is on average like 2.5-3 so you only cast 1.5-2 cards on average. Actually it might be lower since 2.5-3 is when you'd expect 1 land, but it's not necessarily the last of those cards. Hmm.
With 30% dragons or whatever, it's 30% to cast 1 spell, 9% to cast 2 spells, 2.7% to cast 3 spells, etc. so your EV is around .6 cards per turn? Again assuming infinite mana. Wait, I'm wrong - it's not 30% for exactly one spell, it's 30% for at least 1 spell, so it overlaps with the 9%. So it's .3 + .09 + .027 etc, so more like .43 cards per turn.
Up to 50% dragons, it's easier math… .5 + .25 + .125 etc which asymptotes to 1 card per turn, hooray.
All of that also assumes no top deck manipulation and again, infi mana.