Onana might be an average shot-stopper, but whether you like it or not, that's not a priority anymore in modern day club football, for teams that want to keep possession, dominate their opponents, play out of high presses, and build out from the back. And Onana is exceptional at the qualities you need from a modern day goalkeeper. He could start for both City and Arsenal and he wouldn't be a downgrade on what they currently have. Wanting a world class shot-stopper between the posts is completely fine...but not realizing how valuable Onana is and disregarding what he brings to the table is totally brainless.