Buying butterfly as pos1 against high magical damage
So I watched Qojqvas recent terrorblade game, where he bought butterfly even though the enemy has 70% magical damage. That means that 70% of it will pierce evasion, and wouldn’t be a better option to get Daedalus for example? For butterfly if would mean 35 damage, + 30 damage, + 30 attack speed while Daedalus would give 129 damage with crit multiplier.
Am I missing something? Does the illusions gain damage from agility but not crit?