The thing about the other gantz team is that there not doing it as means of survival. For them it's a sport, a new sort of high enhanced further by the drugs. It's sort of like how Izumi wanted to get back into the gantz team so badly simply because he had nothing else to look forward to in his regular civilian life. You can tell that the simply choose to continue playing the game rather then go for their freedom by their choice to gain the more powerful weapons rather then leave. Those new weapons we saw them wield earlier are probably a sign of their progression.
Same rule applies to kurono as well to a lesser degree. At least before he started fighting for Tae.
My guess is that the whole gantz thing is reflective of a larger world wide pandemic. My guess is that for whatever it was created as a system to use civilians to police aliens who were living on earth but it seems as if the scale of both the conflicts as well as the number of aliens fought has increased with each and every mission. Although I just love it how the new gantz team is just a brutal and horrible as the aliens themselves. Because the sort of morality behind the gantz missions has always been something that's been toyed around with, that maybe the aliens might just want to live peacefully. But I think it's becoming more and more clear who is taking on the role of the aggressors if there are more teams out there like the new one.
The biggest question still remains though, who created the gantz system and developed the technology what is really going on.
We can see as much that the different communities of aliens are aware of each other as well as aware of the gantz team trying to wipe them out. My guess is that alot of the answers are going to come out the vampires. Can't wait for the next chapter.