With the crop of players Arsenal have signed, I don't think Manchester United will be on a competing level with them, mere looking at these set of guys. although this is the game of football where unpredictability is the order of the day, Mikel arteta can sign all of this players and still get it atically wrong, last season he had good players that he could actually use to win the premier League and even the champion League, but at some point, he was not getting it tactically right. However on the flip side Manchester United could probably with this few signing they've had, go on to win the premier League who knows, because that's how football works. So getting all this players is not a guarantee for arsenal to conquer the entire Europe.
This is what every Arsenal fan have been wishing for, Gyokeres is a very good baller, a better upgrade to Gabriel Jesus that would finally add balance to Arsenal's squad after several seasons of playing with a complete finisher, well this would give them a boost when they play against Manchester United, I have no doubt that their team has been more solid but don't forget that Manchester United are also strengthening their squad, they've signed good Premier league proven players and would still make more additions hopefully before the match against Arsenal, so it's not something we should conclude that Manchester United won't be a match for them when they face eachother.