All managers make mistakes so did Mikel Arteta. He did not recruit suitable cover for Martinelli and Saka. This season Man City are inferior, Arsenal had space to win the PL title but Liverpool blocked the way. Mikel loves Arsenal, he will recruit in the summer to make them stronger.
Arteta should be given more chance for me he is still doing well as Arsenal manager despite not winning English premier league tittle but they are making progress to that every season and if they continue been consistent like this they will one day be the English premier league champions with Arteta, if not for their inconsistency towards ending part of the season Arsenal would have also won the English premier league with Arteta.
One thing you should also know is that in football ones the team is not doing well they put the blame on the manager if a team is also doing well the manager will be the one to eat the glory so that's just the nature of football.