Assuming Gantz doesnt send everyone out randomly, why do you think he would send Takeshi, who's the weakest Gantzer, out before anyone else? I think it would be because one of two reasons:
1. Gantz is tired of him crying and wanted him to get killed.
2. Gantz wanted him to score so he set him 1v1 against an alien, because we all know if Kaze was there he wouldnt let him get into that kind of danger.