It's not pointless. He was man of the match against the best team in the world in the most important match of their history (and they're possibly the greatest club side of all time) whose game heavily involves pressing their opponents in their own half, trying to win back possession as high up the pitch as possible. You noting that Onana still lost the game despite his great performance (What could he do about Inter's forwards not putting away a single chance?) clearly signals that you've chosen to go with a certain narrative, and nothing will change your mind, however:
Onana's most valuable qualities are being a great passer and his incredible press-resistance. If I recall correctly, even Pep said that trying to press Onana is useless because he's so good at resisting it.
These days, almost every successful side has a manager that heavily copies Pep's style of football and his principles. That means every one of these teams need a goalkeeper that has these qualities.
I'm not saying that Onana will ever become a world-class shot stopper, or someone like Alisson or Neuer, who at the peak of their powers were incredible at everything a keeper needs to do, but in a possession-based side, that's actually a well-oiled unit, Onana would have to make saves with a significantly less frequency. That's why Pep has had Ederson as his number one for 7 years. Not among the bests at shot-stopping, but a great passer, great with his feet, etc. the same strengths that Onana has, and Pep wouldn't have it any other way.
Ederson has faced 51 shots in the PL so far this season, and has made 32 saves. Onana has had to make 72 saves, because he has faced 100 shots already.
If Onana can make the howlers go away, and we progress as a team, not only will he not be a hindrance, he can be a great asset to the team.