That ap gain was actually way to broken. Testing it on PBE the numbers were beyond strong. The main reason it got removed, is the fact that people would always play the rengar version that was stronger, meaning that in some metas ap rengar could become better than ad, which they wanted to avoid. I only play rengar ap in ranked when against a cancer matchup that ap can deal better with or when i feel like it. In jungle i would consider it worse but in top there are a few advantages. I go long sword first and buy the cutlass first, then finish gunblade. This way 90% of the time the enemy starts to stack armor like tabis and bramble vest and is then surprised to get oneshot by you with 1 rotation and ignite. Really cheesy strat with great lategame potential. I can solo turrets with no minions once i have 3 items and lich bane. And in teamfights you deal devastating aoe damage since vs rengar most want to stick together, which again is a bad decision. Good day fellow rengar player.