I don't know if this applies anymore, but whenever I played Coop post 2.0.0, it was less "hey let's cooperate and i'll flying you around yay"... yet it was also less "hey let's speed through the level as fast as possible" at the same time.
A lot of times, yeah, we'd be going our own ways... but half of it was that you'd be exploring the levels and be talking to people also, maybe even observing the others around you (F12 is an absolute wonder). You'd have some splitting up the tokens and stuff, but I noticed people were generally fine with waiting around, especially since if they knew people would be taking their time that you'd also take your time trying out new paths or just exploring/messing around in general. In particular, me and another person or two often will be trying out a new wad together, commenting, exploring, and generally having a fun time.
Yes, it's the same things you can do in single player... you could also play Garry's Mod in single player mode just as much as you could multiplayer. But SP Garry's Mod is very boring... MP is an totally different story, even if it's just so you can observe what everyone else is doing and talk to them, too.
Of course, considering how socially I can use SRB2 sometimes, it's a wonder I haven't been banned from the MS for not playing super srsly. Then again, I usually only play random new coop wads or play on CTF servers anyways.