Even De Gea definitely continues to get entertainment when watching his former team compete because they have always had bad results so far. That is real karma for Manchester United because they have thrown away an experienced goalkeeper like De Gea and preferred a goalkeeper who was only good for one season.
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, but however every good performance of a goalkeeper always depends on the good performance of the defenders because even with the highest goalkeeper in the world could perform very low if the defenders fails to do there work very well so in Manchester United that's what they are facing, how would they expect Onana to perform well as goalkeeper when the defenders are not helping.
Firstly I would want us not to dwell so much on the past it's not helping the present, Onana has a record which has been fantastic but that's in the past and we can't continue to glorify the past and make it a good reason to excuse the present failure, success is more appreciated when it's been sustained and repeated over again regardless of the circumstances attached to the success.
Going by what you are saying it means Onanas success was greatly dependent on the defenders and now that those defenders are no more his blunders are been exposed of which it shouldn't be so, no doubt the presence of good defenders aids the excellent performance of a keeper but then the keeper himself must have some level of accuracy that will be complimented by the defensive efforts, so we can't blame it so much on the defenders.
De gea was in Manchester united with these same defenders although only but a few has changed but de gea did well with these same defenders onana is having a hard time with so I think it's time we stop excusing him and bring it to him that he is been failing the club and should improve, he doesn't need the whole season to prove how good he can be. De gea is also doing well where he is now with new set of defenders so I wouldn't want to start comparison now as there will be More than enough to talk about as it concerns these two keepers.