Agree with kevlarman.
2 bsuit/chains can take down a good tyrant.
2 good shotties with helm/armor can take down a tyrant even quicker.
Wrong. Chaingun is much faster. It deals nearly 50% more DPS than shotgun ( without counting the shotgun reload )
As for why the humans camp, I see two reasons. I do not take into account the sitations where humans camp but shouldn't. Those often happen because of a lack of information on the current situation.
Not really, when aliens have too many tyrants around, attacking the alien base is rather futile. It's not really that you'll all die doing it but that you'll never reach the alien base in good enouth shape that it matters.
See, no matter how big the human strike force is, if you face a reasonable Tyrant force on the way to the alien base, you'll most of the time lose a lot of ammo, health and a teammate or two in the process. For the humans attacking, such operation is very bad. Of course you've maybe killed a few tyrants, but you are now in no shape to continue going to the alien base, and some humans were killed in the operation.
So, from the point of view of the dead humans, you had a completly failed attampt at attacking the alien base which ended in them losing all their hard won equipment. No wonder they do not want to do that again. If at least the rest of the strike force had the ressources to continue forward and deal some damage to the alien base, it wouldn't feel like such a waste. So in the end, humans only attack when they know they can reach the alien base unhindered. It often requires reducing the whole alien team to dretchs, or sneaking around to their base.
Waiting for such favorable situation represents 50% of the human camping problem.
Now, the other reason humans camp is because they cannot expect to win the game without a base. And a human base will only hold a few seconds against S3 aliens unless it is defended by several well equiped humans. As soon as there is a good Tyrant and a good Adv Goon nearby, you HAVE to stay around and defend. It requires at least 2 humans, one to repair, and one to scare away the aliens. Get more aliens and you require more and more humans. Aliens situation is less critical. They can lose the base and they still have good chances of surviving provided the warriors are still alive and with higher evos.