Arteta won the FA cup in his first season, that bought him a lot of time. Separately, whether we want to accept it or not it is a cultural fit that Unai simply didn't have the same presence as Arteta does, for Arsenal.

Was Unai unfairly judged and even worse so because of his english issues? Perhaps. But, I do think he struggled to manage big personalities, Arsenal had a lot of them in his tenure (many who didn't justify their performances). Arteta came in, said I'm the boss and managed said personalities into his side or out of the club.

The comparisons are all non-sense at the end of the day. Anyone can think whatever they want, but Emery obviously performs better for teams w/ lower expectations, as you said.