Again it depends on how he leaves the club. This was the same argument with Ole when people said he will leave the squad in a better shape, but then he continued to stay and left a more , how to put it, complicated task for his successor. He should have left at the end of the season before, after the europa loss to Villareal and he would have been remembered much fondly.Yeah I'd agree with you here, it's his squad now.
Fair enough.
Don't get me wrong I do believe that there are plenty of other managers in world football who could have done a similar job.
The problem is convincing the ones who could do a better job to come to Arsenal.
If it all goes pearshaped for Arteta this season I really do believe that he will leave the club in a better place than he found it (comparing the squads /obviously paid large amounts of money for but that's Football) and the next manager will have a higher base to build from (and if they discover the next Klopp could turn them into a Top 4 club).
Same could happen with Arteta. The likes of Saka, Martinelli, Tierney may say enough is enough and we want to leave and play CL. This is why they have to be very careful. Things change pretty quick in football.