Onana is over rated because he has better passing skills than De Gea but in general, combining all skills of a goalkeeper, I think he is not a better goalkeeper than De Gea. Hopefully Ten Hag will not have to pay an expensive cost by his coach position because of his belief in Onana.
I keep hearing that Onana is good with his feet and that he can pass the ball, but TBH i don't see that when i watch Manchester United's games, he is average in his usage of his feet and his passing accuracy, he is nothing close to the likes of Ederson of City and Allison of Liverpool when it comes to passing accuracy.
It is also worth noting that Onana has lost some amount of confidence since he joined Manchester United. And this has affected everything about his performance. If we take a look at his performance in Inter Milan, I don't think we would doubt that the Cameroonian international is very good with his feet. As the Manchester United squad keeps improving we might also see Onana giving that his masterclass passes..
That being said, Onana is not a great goalkeeper IMO, average at best, and i think United made a mistake letting De Gea go, the Spanish keeper is better than Onana, De Gea makes unbelievable saves, even though he makes quite a few mistakes too, as for Onana, he doesn't make great saves, but still makes mistakes leading to goals; i'll take De Gea anyday.
Manchester United is going through a lot of problems and we cannot say that its players are having a good time. When a team is not doing well, it is the goalkeeper that most times bears the negative effect. Onana is still young and needs more time to gain experience and exposure. De Gea is 33 and has played more games than the 27-year-old Onana. I still have confidence that Onana will soon get used to the EPL and United will know that his signing is not a blunder.