There are several players who are actually good enough for Arsenal and are on the sales list right now.
Partey is one that allows to be let go at this time. He is a pretty good player but injuries always affect him in playing. On the other hand, it seems that Arteta also doesn't want to waste time. Caicedo and Rice really seem to be projected for next season for Arsenal's midfield.
Arteta's faster movement in finding new players to replace old players in several lines is quite natural, because Arteta doesn't want Arsenal to suffer another ridiculous defeat like what happened this season. So Arteta chose to move more quickly to make the Arsenal team stronger next season by recruiting several good players to be placed in the lines they need to be strong from the start of next season which of course can also target champions at the end of the season.
Arteta should start seeking players and give the list to Arsenal and help the team to hire players as fast as they can because they have to race with a team like Manchester City in the next season with all the stars they have.
I agree with you that what Erik Ten Hag has done for Manchester United this season deserves appreciation. We also have to remember how Manchester United were before he arrived, and even at the start of the season they had a losing streak which resulted in them being at the bottom of the table at that time. But slowly they can get up and can collect point by point to take them step by step to the top of the standings. and in the end they can be ranked 3rd, it is an achievement for them.
Manchester United also won one title this season, and that was a good start for Erik Ten Hag to bring another title the following season. Don't forget too, they felt the internal problems of the club which disturbed the balance a little, but they managed to get through it well.
I think if Erik Ten Hag is given a longer chance he can revive the championship passion of Manchester United.
The second season for ten Hag will be decisive - it will no longer be possible to blame everything on his predecessors or on Ronaldo. Although I support United, I think next season will be worse than this one - just at least due to the fact that Liverpool and Chelsea will return to business (presumably) and in such conditions even getting into the top 4 will be a very difficult task.
In this season when we saw the game between Manchester United and Liverpool and Ten Hag lost with bad results I saw him doing the best he can do, Ten Hag punished players by making the player watch Liverpool celebrating which can be a good shock for the player to have better performance.