I wouldn't call your eyes "healthy", given that they see Onana as disastrous but DDG last season as quite good given he was, both to the eye and according to statistics, even worse. This is the problem with relying on the eye test - you're clearly looking through a biased lens that will lead you to overrate the player you like, and underrate the player you don't. Stats help the more rational among us temper that bias with objectivity.
It's widely reported how almost all of the big clubs have embraced data to make decisions, and how the role of scouts is changing. Even we made a big push towards being more data-driven when Murtough took over the footballing department. You may want to remain in the dark ages, and that's fine, but football is leaving you behind.
So, basically what you are saying is that we are all blind, our eyes lie and Onana is really good.
How is what we actually see a biased lens.
I get the impression that you don't know how data and stats work, where is the benchmark for his performance this season, you cannot base it on last season, because he wasn't in the Prem, so the data is flawed.
You cannot base it on his data at Inter, because it is incomplete, only 24 games played last season.
I would agree with you if;
He wasn't making the same cockups he was at inter
He wasn't making the same cockups he was at Ajax
He wasn't making the same cockups he was at International level
He has the same defence in front of him that De Gea had last season, and he's only got 8 clean sheets against De Gea's 17
Or perhaps you've forgotten we tried to sell off Maguire because he was so bad last season, Varanne spent a lot of time injured, Martinez was out for periods, why do you think we signed Evans in the summer?