You are right Arsenal's weakness is in the second tier players when Arsenal schedule is tight and one of the players is injured then problems can occur so Arteta needs to focus more on problems like this. This season Arsenal have brought in 3 players Midfielder, Striker and Defender now their strength is almost equal but I'm not sure if the current squad is enough to go through all the games I think Arsenal need a few more players. Arsenal are reportedly planning to bring in a midfielder , Mohammed Kudus is on the list but it looks like Arsenal do not have enough funds.
Arteta himself said he’s still expecting more players in and out. He want to add another attacking player to their squad to deepen the options in attack. The starting front three of Bukayo Saka, Gabriel Jesus and Martinelli is already supported by a host of options. For now Now, Arsenal have more quality options in attack with Trossard, Eddie Nketiah and Reiss Nelson available to provide healthy competition from Bukayo Saka and Gabriel Martinelli.
Kudus is capable of playing as a centre-forward, out wide on the right or the No.10 role. But right now, those positions simply do not need strengthening. So I don’t see Arsenal adding him to the team again even though he’s a versatile player.
I think there are a lot of mistakes in Arsenal's game planning. Besides, I really have no idea how the coach of the team is taking the team forward. However, the Arsenal team has the ability to perform well.