Just in the League:
Ozil missed 12 games
Ramsey missed 15 games
Wilshere missed 14 games
Walcott missed 24 games
Cazorla missed 7 games
The fans complain about depth and when a player of great quality might be signed, people ask why. People asked why we signed Ozil when we had Santi. It baffles me because you want to have a squad with the best players. You want to have a squad with depth. You want to have as many great players as possible. It baffles me when people question signing a great player.
You also get the "where will he play or the squad is full" type questions. That was the case with Ozil. It's the case with Cesc. If you have great players, you make room for them. Heck, Ramsey wasn't supposed to play at all this season because Jack had "solidified" his place. Ramsey was the revelation of the season. He played himself into the line up and kept himself there to the point where you couldn't take him out because he was so much better than the guy who would replace him. What happened? He missed half the season. It was just too bad we didn't have another player good enough to give him rest so he wouldn't get injured. It was too bad that we didn't have another player to give Ozil a break instead of him getting worn down because he had no breaks.
If Wenger buys Cesc, then it will be up to him to make everything work and finding a place for him to play and rotating the squad to get everyone games, but to me, I don't think this is a "least necessary" move at all. There will be plenty of games available and I think Cesc can again contribute a lot to Arsenal.
This is not to say that I would be satisfied with a Summer of just Cesc, but I think it's far from the "least necessary" move Arsenal can make. I see it more as solidifying something that Arsenal is great at. My one worry is that this becomes a distraction because the team really needs to get 2-3 deals done for good players on top of replacing Sagna.