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.
This season Arteta did a very good job by fetching out the best player that made the club performance great. Arteta will definitely bring good players that will be in a better replacement of the players that are no more in the team. I don't have any doubt I just know Arsenal performance will be much better in next season.