Indeed De Gea was one of the best goalkeeper Manchester United has ever had but I wouldn't blame the club for going for Onana because Onana is actually a nice goalkeeper and has been doing really well since from when he was keeping for AC Milan, I think from his past records, he has more good quality performance than De Gea
Since when
Onana played for AC Milan?
He played for Milan but it is Inter Milan and in the last season, he had a Champions League final with them. Before playing for Inter Milan, Onana played some seasons for Ajax Amsterdam where Ten Hag worked as a coach. That is one of reasons Ten Hag brought Onana to Manchester United like Martinez.
Comparing Onana and De Gea, if it is only about saving ability, De Gea is better. If it is about passing, in theory Onana is better but the yesterday match with Galatasary shows that Onana is not too good with passing. With a goalkeeper, is passing a most important skill?