I somewhere agree with you based on his history. But there is a part of me that thinks he may have just been unlucky.

He was at PSG which was a mess with players having more power than him. Then he went to Arsenal where he had to replace Wenger which is poisoned chalice. He also inherited a relatively poor squad which includes the Ozil situation. Then on top of that they weren’t giving him the players he wanted. He wanted Zaha, they bought Pepe etc

So he might still be a top level coach