Yi currently sits at a 51±1% winrate in Bronze elos. This isn't something I call "too strong" I'll give tips though.
His Q doesn't do tons of damage, it needs to be paired with an e or basics.
His W is mediocre and leaves him open.
I can agree the ratios on E are a bit high
ATM. Maybe a decrease in affect time will help.
His R is for Slows, not any other CC. Hit him with a stun or root.
You need to build core items to save a game. If he builds lifesteal, your ADC should get a mortal reminder. They're gonna die, but you can hit them down for a bit. AD mids or tops that aren't tanking should take this item instead of your ADC.
Attack speed can also be handled. Have your tank buy Thronmail and Omen. His basics will be slowed and the grevious wounds will be applied. Your tank COULD build armor to buff up the damage from your thornmail, but I just use it for wounds.
Your team won't have the necessary gold to build items before You will start ganking. The current meta punishes AFK farmers and expects you to gank early. Try to secure a kill on him quickly. If it's 5 minutes and he has no kills, capitalize on it ASAP. Steal his jungle and if you go leathality, consider a poachers dirk.
You also need viable picks against him. One would think Jhin or Caitlin is a smart choice because you stay back, but they have low as, pitiful lifesteal, and no escape mobility (unless your dirty and go Crit Jhin).
If it all works he'll be useless. For added effect, BM him each time he dies. Emotes will make a player VERY angry because they are so used to winning with him. You'll either make him start a war with his own team or he will just quit. Cheers!