Why do people complain about Lee Sin when Jarvan IV is better in 99% of situations
At least outside of competitive play.
The only place where Lee Sin is top tier right now is in places like OGN and maybe extremely high Challenger MMR.
Everywhere else you'll have much better luck using Jarvan, he's way easier to use, gives a ton of auras for his team even if you mess everything up, is innately tankier, is way more useful late game, and is just more reliable period. Lee Sin hasn't been relevant late game since they removed his attack speed slow (because aoe 60% attack speed slow was broken late game).
Stop picking Lee Sin in solo queue, you most likely will lose with him since you can't use him well.
This Lee Sin circlejerk is so pathetic, he's not even good in where most Boards or LoL forums play in anyways. You can keep QQing about Lee Sin while Jarvan players will collect their freelo and probably remain unnerfed