De Gea was a fantastic player for us. To overcome those early challenges and become one of the best keepers in the world was a testament to his ability and character.
However, it was clear (probably post 2021 Europa League final if we're being honest) that he was no longer good enough for the very highest level. At that point, we should have signed a replacement or trusted Henderson to be number one for a year and sold De Gea whilst there was some demand for him. The fact we didn't is probably as much to the club's instability and lack of decent scouting. It still seems mad that we gave Henderson a five year contract whilst keeping De Gea. Lack of strategy again...
It was also clear that even in summer 2023, United still believed De Gea was the best option. When the contract didn't get signed, we had very few clear options. For all his faults, Onana (on paper anyway) had a decent track record to be his replacement. It quickly became apparent that he wasn't up to it and now we're in a situation where we've gone so far downhill that a keeper who wasn't good enough 4 years ago probably is just about good enough* for our current situation and is better than our current two keepers.
*That doesn't mean he's good enough now just a sad indictment of how bad our recruitment is.
The same can be said for Fred, McTominay, Elanga etc