Yi is a low level pubstomper. Using your smurf as credibility for your claim is like basing warding standards on a Bronze adc who thinks it's the support's job and only their job.
Okay, that was a bit snarky, but you get me? You get one champion with a knockup and there goes Master Yi's heal. You get one champion who stacks well with health and his true damage means nothing. You build thornmail and there goes Master Yi's right-clicking mastery. The second he highlanders, hit him with a stun and watch it run out.
People, including smurfs, spamming him every single game pre-level 30 has ensure that by the time people hit level 30, they know damn well how to counter him. He's strong, he's easy to pick up but hard to master, but he certainly has his counters.
He may be a hypercarry, but he's got enough counterplay that he really doesn't faze me. When jungling, and I'm against a Yi, I just drop a ward at my buff, wait for him to try to steal it (because god forbid a Yi gank when his jungle is out of camps), then assert my dominance.