User blog comment:BIA-Kaboose/The Problem Behind Balance/@comment-5883057-20131211130411/@comment-1330314-20131211200704

AP Yi wasn't removed because he was overpowered, he was removed because his style of play was toxic: his rotation in lane relied on poking with his Q for massive damage and healing away any health he himself was missing, with no possibility of counterplay to him. In teamfights, he was also super binary: either he could chain Qs and instagib the enemy team, either he didn't deal enough damage and ended up being useless. The current iteration of Master Yi is stronger, but also healthier (at least now): he can still poke in lane, but he doesn't deal the same amount of damage from his abilities. Instead, he has to rely on his strong steroids to keep himself going during teamfights, and use his W strategically instead of healing away all the damage he may have taken. Riot changes champions not just in terms of power, but also in terms of gameplay healthiness: what is good for the game is encouraged, what is unhealthy gets changed or removed.