well, ive seen champions go rampage with devourer that dont even have on-hit effects more than i have seen those come-to-mind on-hit champions dominate.
i havent seen master yi be so much stronger than before, i havent seen kayle be such a good jungler now, i havent seen anyone benefit from this item very much yet.
even tho the damage is really high now after 30 stacks, it isnt high enough to swing situations that were unfavorable for any of these champions into a favorable situation. like, if you fight to the death and you survive with 30 hp, it might have been because of this item, but then again, who cares about these situations. if someone facechecks/gets caught by a yi, he dies regardless of what jungle item he went or whatnot.
really all it does is add a little bit of extra auto attack damage to players who get to auto attack alot through good positioning and gameplay. auto attacking is actually one of the hardest things in league due to all the CC and jumps, especially for champions who have no cc themselves. sure, auto attacking with irelia doesnt win a prize, but if someone is able to stick to a target in a teamfight with master yi, either he done good and deserves the damage he dealt or the enemy team was brain afk. even tho the latter happens quite more frequently in soloQ, rewarding constant auto attacks doesnt really break the game.
i mean people cry about everything, but i think its kinda balanced.