Different Gantz have different rules? Reasons why things are done this way.
Do all of the Gantz have the same rules that the Tokyo Gantz does? Are there allowed to do things however they wish as long as the job gets done?
I'm curious why Gantz doesn't see all those dying, and decide to bring back everyone who has ever earned a certain number of points before. He would thus make a better team. Of course, they do win most of their missions, there only one failure so far, that when just one got away, so it doesn't really matter.
Perhaps this way he gets to test out more people, and when the time comes when there is an absolute need, bring back all the best hunters.
Could it be the Osaka team members are not afraid of dying, because their Gantz has initiated a policy of automatic free resurrections if any die after earning a certain number of points? That would explain their attitude.
Eliminate the fear of dying, and it could either make people into fearless warriors, no reason for them to not fight to the best of their ability, or it could make them arrogant pricks who don't take things seriously when they should.