Is Master Yi most powerfull Champion in LoL?

Yi, Katarina and Darius are definitely the easiest champs to get a pentakill on. I don't think any champ in the game spikes harder than Yi does at three items, it's just ridiculous. I think he's the strongest duelist in the game at that point, maybe matched by Tryndamere, and that's only because trynd has his ulti. If Yi can bait out the ult he'll win every time.

In terms of general viability and performance though, Yi is actually a relatively weak champ. He still stomps hard in lower elo though.