Well crouching is not only meant in real-life for aiming better but also for the following:
Imagine you are in a war zone as a soldier: What would you do when you stick to a wall?
Look up and bring your head into the shooting fray or crouch and being secured from the wall thanks to not getting headshotted by a possible sniper that could aim for your head as soon as you are on a look out
!
For me the answer is simple and obvious, therefore I would say that crouching is fundamental in a fps even if it is not meant to be there for the predator crouch jump thanks to his new jump mechanic.
This accounts even more so in DM when there could be scenarios with marines vs marines. I think crouching would be quite useful then but maybe that is just me
... .