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.
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.