In that case, youre effectively playing with a 56% chance to win (80% * 70%), which should be better than a mulligan
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If this happens, not only does the chapter ability you landed on trigger, but any ones you passed along the way
Regardless, I dont know that now is the time for more than 60 cards, but I do know that as the card pool expands, it gets easier and easier to find more spells of a similar power level, but no other lands are close to the power level of fetchlands, so the incentives to build to maximize the power of our lands over the power of our spells do increase in some way over time, which is to say that, even if its not right now, it could be someday, and getting there first might be the best way to truly break Modern.