You removed DFG, now remove Infinity Edge

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The fact that you can use the active of with only half the item built ( ) is still a huge advantage to AP users. AD users would kill to give the active of

I see what you're saying, and you have a point. But the fact that you can activate it "only half built", as it were, is only an advantage until you reach late game; at which point AD users get a full item with insane utility and AP users have to sacrifice considerable damage for utility (or vice versa).

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On the other hand, you really can't activate while a ult is flying at you. I'd call it pretty even.

True, but you can flash away from that Ult. Or dodge it through other spells.

Obviously, you may not always manage, but you have a chance.

On the other hand, with Zhonya's, the second you're stunned (or silenced? I forget), it's over. Sure you can probably avoid a stun with Flash/ X ability as well. But 1 ult has a long CD. Stuns typically don't, and there are usually more of them. Furthermore, when you use QSS to escape a stun, you can move/attack/heal/whatever immediately. You're still useful. You can still escape/ survive/ kill/ help/ whatever. When you use Zhonya's in an effort to not get stunned or destroyed by, using your example, a Syndra ult, you're going to be in the same spot for a while (and not doing anything helpful, typically). Using Zhonya's well may result in an emery blowing a big damage CD on you for nothing, but it leaves your team in a 4v5 for a little while (except in the case of fiddle/ Swain ult/ are there more?). With QSS, you take the damage but you can return to fighting/etc. as I said.

IN SOME CASES Zhonya's will absorb damage from 80% of the enemy team's big damage spells. And in those cases, Zhonya's > QSS. But that doesn't happen often enough to make Zhonya's active more useful than QSS', in my opinion.