All the heroes from the game have counters.
Search the forum for other posts and you will see many players explaining about how to counter Ezio.
It's not there is no counter to him or that hw is super strong but the fact that he literally is able to get out of ALL mechanics in the game. He is the only hero that can do this and it does not state anywhere in his skills that he can shrug off any crowd control and ultimate in the game.
There is, and is this easily observable by the fact that most top teams in arena do not use him.
He is strong versus some types of teams, and this is indeed due to the fact that he is able to dodge a lot of stuff. But like I said that is his strength, are you suggesting that he should have no strengths? Because if you remove this from him he will be useless. He already is very squishy if he finds himself in a position where he can't dodge. If you remove his doge he will die in 5 seconds to almost everything.
Try aracna, she is one of the best counters for him. If he is the tank he is dead meat, use aracna on the front as well (usually I don't advise using aracna on front). If he is not on front and he manages to use an ultimate on her... both will die, so that's not so bad as well.
There are other heroes that are good vs him: most magic ultimates, cara, dokras, etc. Although dokras is widely mentioned I don't find him to be that good of a counter, the trap is a hit or miss vs ezio, sometimes it works sometimes it doesn't, but cara almost always works and he dies instantly.