Reset mechanics are too hard to do right
Pseudo reset, extremely unbalanced when strong. Can chase everything and everybody, hard to immobilize.
Immense speed boost on what's usually an immobile hypercarry, takes over fights and has tools to secure kills easily from afar. ALWAYS relevant in every meta simply because of crazy range and ult.
Similar to Akali, only less mobile and stronger resets.
Remember when Kha'Zix was stupid broken? That had to do with his insane poke, but people are forgetting that he poked and then could just jump in and out and resume the pattern. He still has a crazy reset pattern, which is evident when his numbers are high.
Old Yi. 'nuff said.
Same as Jinx, only safer early game, weaker teamfights, and more mobility / self-peel.