Yes, the FPS term is "camping", "turtling" is an RTS term for someone who spams defensive structures.

I notice this too, I'm trying to figure out WHY. Is it because humans usually lose to an alien 1on1? That's definitely the case for me. As a dretch, I'm confident that I can kill a lone human, unless maybe he's at the other end of a narrow hallway and has lots of time to spray. But as a human, unless you spot an alien from far off (doesn't happen often in the tight indoor environments), it's at your ankles before you can get some shots out at it.
My human n00bishness aside, I think I know the problem. Aliens can go anywhere because if they're low on hp, they just head to a dark corner and wait 20 seconds and they're healed. Humans, however, only have one "regenerator". Which leaves them tied to their medipad all the more.
I think a reasonable solution would be to have a "pack" item called the medipack, that enables humans to automatically regenerate health the same way aliens do, but at around 4 hp per second. To make humans less alien-like, the pack would need to make noise when active, to force the human to back off much farther to find a safe place. Making it a pack upgrade ensures that it can't be used by jettards or battlesuiters, keeping things balances all the more. If you ask me, this'd be a better alternative to the "medic" class being considered, although that has its bonuses too.