No it's you who is missing the point. Ederson could become a better goalkeeper. You seem to think that because the team is successful, there's no need in your mind for him (or presumably any other players) to improve.
That's not the case. There's huge scope for Ederson to improve his game. He has significant gaps in his basic skills.
As a professional sportsperson, he should be working on them. If he has been, we should see an improvement on his all-round game. But we haven't. He's still cautious in his six-yard box and reckless outside the penalty area. That leads me to think that he doesn't see any need to Improve his own game.
That's arrogance in a nutshell, and if Pep is prepared to accept it, Ederson will never be a truly great goalkeeper. If you and other fans are happy to accept it, that's your perogative. I just believe that Ederson should and could be a better keeper if he works on the basics.
It's the simple things that make a big difference.