So Arteta doesn’t get the best out of his squad when he doesn’t have a full team. But he’s not unique.
Both Pep and Klopp have been able to get to 100 points when they are able to get full seasons from their very best players. What happens when these players are injured. Wee saw Liverpool drop like a rock last season with VVD and others injured or out of form.
City are even more interesting. With a healthy team with Rodri, Gundogan, KDB, Haaland etc, they wheeled out 18 straight league wins and got the treble last season. This season with KDB out for all the games they have looked limp, they’ve lost every game Rodri has missed, and have struggled in most of the games without Haaland. And they’re on an 80 point pace, not their typical 90-100 because of this, despite having a deep squad with players like Grealish, Foden, Doku, Nunes, Kovacic etc who can fill in.
All this tells me is that depth isn’t as important as your peak quality. What really matters to a team is having superlative players available as often as possible, and being able to coalesce around them. And not even Pep can transcend this.