So I have figured that since you can play with friends, wouldn't it be logical to add a Co-Op with 2 or 3 players?

The thing is, sometimes you and your friend don't end up in the same server, and one of you might have trouble with wall clips and such (when you're doing glitched).

probably

you just need to hope you end up in the same server

I'll think about it

the only viable place to use it is in c3 and maybeee if someone does a fighting queen category... so it's pretty much not that useful?

In Glitchless they can help each other out with the code doors in C2 and C5.