Yasuo is a much bigger problem.
At least the team has to work to funnel their power into Yi for him to be effective. It's still disgusting and shouldn't exist, but I've seen so many Yasuos somehow feed their butt off the entire game despite his versatile kit, then just decimate teams late game with no effort.
I don't even like having Yasuos on my team because they feel so comfortable feeding.
They'll take every bad fight for a chance that they'll win it because it doesn't matter to them.
Yasuo is going to be a threat late game regardless of how they perform. Meanwhile, the rest of the team takes a huge hit because that reckless player is mindlessly giving away so much gold, usually to another assassin which makes you play super safe and fall further behind.
We get no chance to even try to win the game ourselves with most Yasuos in solo queue, and I'm sick of it.
Those players force you to rely on them even though they're the reason you're in a desperate situation.
All you can do is turtle the match while the enemy team sweats to win a match they realistically would have won already if we didn't have Yasuo on our team. No other champion can hard feed and then turn into massive threat.
What ends up happening is the game turns into a drawn out coin toss all because of a bad Yasuo player. It's happened numerous times to me, but I was reminded of this frustrating situation after I had a Yasuo on my team go 0/8/1 by 17 minutes and then got a triple kill out nowhere. Nobody could contest him, and we were forced to play to win while they try to figure out a way to get around the Yasuo.
The only one having fun in those kinds of matches is the Yasuo player.