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?
Passing isn't the most vital ability for a goalkeeper to have, but knowing how to pass properly gives the team an advantage, and goalkeeper’s won't make the same careless passing mistakes that Onana did which cost them a penalty against Galatasaray. When comparing these two goalkeepers, what matters most is their ability to save, the one with the better clean record should be the better of the two. When compared to goalkeepers who are competent at goalkeeping, a goalkeeper who cannot save his side from goals should not be held in high esteem.
Arsenal might suffer against Manchester City cause they'll be playing without two of their key players Martinelli and Saka who are out due to injuries and would need creativity in their attacking line to be able to beat city's defense, Pep Guardiola could take advantage of Arsenal's lose and come up with a strategy that would make them score more goals, against Arsenal.
This was supposed to be a very intriguing match if both clubs had their full squads. Unfortunately for Arsenal, two of their key players are out due to injury. Manchester City is quite effective at exploiting their opponents, particularly its closest rivals, like in the case of Arsenal. They will not give Arsenal enough chances to take control of the game, and they will do everything in their power to win and keep their place in the league after losing their last match in the Premier League to Wolves. I still expect the game to be exciting, but it will depend on how Arsenal performs on that particular day.