Master yi design doesn't make sense.
Before you go "omg yi nerf, gut him" go look for a teemo tread and have fun.
Yi play pattern is an assassin one. He works better cleaning up a team fight and has a reset.
The problem is yi does not have the tools to be an assassin and is outclassed as a fighter.
1- an assassin is generally feast of famine, recurring to split pushing during the late game if his early was weak. See shaco, zed. - Yi sucks at split pushing. He can't dive like trnyda/zed nor he takes the tower fast as jax.
2- An assassin has little to no utility. Zed has a slow, shaco a slow and hard to apply fear, kat has no cc. They get burst damage. Yi has dps. No team utility, no CC whats so ever.
3- A fighter has utility, can dish some damage and is an off tank - jax, renek. Pantheon. Even of a fighter is famine he can do something for his team. Jax can stun, pant cand dive ans stun, renek can dive and stun.
Yi has the worst of both worlds. He wants to be both classes but don't have the tools to do so.
Q- is an engage/dodge tool. Can rarely work as a disengage only if you have a wall in between, since it's casting time allows the enemy to catch up with you. Can rarely work as a poke tool.
E and passive - AA related. Needs to survive if he wants to do damage. Would be great in an ranged carry.
W- generally used as a glorified AA reset. It is a skills that generally a lose-lose situation. Is he alone? Keep smacking him until he dies. It is in a TF? Let him heal and deal with the rest of the team. It is a 4x5 since he is there, wasting his ult and wanking his life back. Or you can stun/knock him up making is more useless than any spell shield that means mitigated damage while you can AA the enemy team. It is a dead skill.
R- low duration. If he wants to splitpush he will have to burn it to escape. When he is on cd master yi is no threat. It isn't like other assassins that can deal great damage without their ults.
Yi has no utility to offer for his team. Any ADC can do what he does in a safe distance, some can even blow up him.
Imagine a vayne, with no CC and melee range. That's master yi.
Riot, If you think he is a fighter, give him the tools to soak up damage while doing damage and some team utility. (Diana) If he is an assassin, give him the tools to go in and out a fight and burst damage ( zed/ shaco/kat)
His current kit makes no sense.
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Also keep in mind if This guy
is their jungler which would be nightmare laning phase for you