When I referenced Poch it wasn't when he came to us, but when Soton appointed him. He had 0 PL experience before Soton. And yes, I did highlight the ones that were successful, because the point I was trying to make was that you can be successful as a PL manager, even if you do not have PL experience. And you can be a failure, even if you do have PL experience.
What makes managers good are the tactics they employ, how they adapt the squad to the tactics and the tactics to the squad and the opponent, how well they read the game, as well as some of the things you do not see in the Youtube videos, such as how well they get across to the players, how well they motivate them, what kind of team chemistry they create. Imo, if on top of all these things they also have PL experience, it's a bonus. But it's not a prerequisite.