I didn't say he was really bad. That seems to be your own interpretation of the criticism on this thread. Some has been very harsh, some has been spot on imo.
I have long said that he's not a particularly good goalkeeper. By that, I mean that (again, in my opinion) there are plenty of better shot-stopping goalkeepers in the game, that I would feel much more confident about at City than Ederson.
It's all about opinions of course, but Ederson won't have a problem at City as long as Guardiola is in charge as his is the only opinion that actually matters.