Nah, he was very solid for BA last season but just can't make a step up to La Liga football over night. He's not a bad player but just pushed into a situation he's nowhere near ready for. Also not used to play this suicidal high line, Marquez never played that risky last season. I think it's still fine and important to start Martin in games like this to rest Balde though. CL group stage is pretty much irrelevant in this new format.
Another thing is how important backline chemistry is. We are doing fine because JK-Pau-Inigo-Balde are playing in most games. So all the injuries are probably a blessing in some way as otherwise we wouldn't have that much consistency in first few months.
We'll see how offside trap will work when Araujo and Christensen are back. And I'm not comparing them to Martin, they are clearly levels above him quality wise but there will be more individual errors whenever a new player will come into that now established defense. It's up to Flick to build up chemistry amongst different (mostly CB pairings as I don't think we'll rotate that much at both FB positions unless needed) defensive combinations if he wants to play this way and prevent the opponents chances to punish us in every game. Because it's clear if they break the trap then it's 1 on 1 with Pena in most cases and I wouldn't bet on him to save us many times.