Do you think Manchester United can compete with Arsenal in the new season? In my opinion, it is impossible at the moment, there is a gap between the levels of the teams. Arsenal was strong enough without these transfers, and Manchester United seems to be in a very bad state and these few transfers are attempts to level the situation a little. So I do not expect any reaction from Manchester United to this transfer.
With or without Viktor to Arsenal, Manchester United are not close to what Arsenal has done in the last few seasons. They are incomparable and are not fit to be on the same trouser but I don't want to use over excitement of Viktor to Arsenal to think they are the best here. He clearly want Arsenal and has rejected other offers and also reduced his wages so they can consider him to the team and now they just did, he is just another potential but that doesn't mean he is going to change everything over night.
Last I check, Amorim was the previous sporting cp manager, he was doing well until he switched path to Premier league and things hasn't been the same and that's because clearly Premier league is very tough and competitive. Viktor Gyökeres has had a good career in Sporting CP but that doesn't uplift Arsenal performance to the top of the table but I expect to see some changes since they now have a perfect striker that is going to do more for the club than they have always wanted.