One of the debates I have heard many times is that such and such player, usually one that isn't all that good but can "do a job", is fine for Arsenal to sign (or re-sign) because they need the depth at the position.
The follow-up is usually something along the lines of they really won't play that much and therefore being able to "do a job" is good enough.
I hope this straw man is at least mostly accurate at capturing similar conversations that you have made or heard
The players that I think have personified this sort of signing in my mind would be Pablo Mari, Cedric Soares, and maybe even the re-signing of a player like Mohamed Elneny.
It isn't that these are bad players (one of my pet peeves is the description of a player that maybe is limited or with clear weakness as shit, just bugs the crap out of me and I hope that I never do that here is writing) they are just not players that if they appeared on the teamsheet for this current Arsenal team, with their current ambitions and goals, that we would not dread seeing there.
So this is where I think the idea of having what I am calling 1B type players matters. A 1B player isn't a guaranteed first name on the teamsheet player but they are a player that if they start they bring something to the team and maybe in some situations are a preferred solution.
I look at the current team and think that there are a few 1A automatic starters if they are even remotely fit enough to play guys. My list right now is Bukayo Saka, Gabriel Jesus, Thomas Partey, Martin Odegaard, Takehiro Tomiyasu, and Aaron Ramsdale.
Last season I would have included both starting centerbacks and Kieran Tierney but I think the addition of William Saliba and Oleksandr Zinchenko have now made both of these spots things that can be optimized for the opponents and how Arsenal wants to play.
This is to me the proper way to add depth to the squad.
At a base level having numbers to cover for emergencies is required but what Arsenal have done here is something more than that, especially considering the hybrid and versatility that Arsenal have added. I look at this team and see choices at positions with multiple quality options that each can fill the same positions but offer the ability for Arsenal to vary the problems that they will present to the opposition.
In a world of five subs this seems like the perfect strategy, each substitution can be a subtle tweak tailored to the game state and time remaining in the match. I am excited to see the potential for what this can mean for Mikel Arteta.