Random teams are fine, like in the Competition arenas. Randomly chosen members for a team in the Tombs, however, will never ever ever be good.
My idea for a good Tombs party:
2-3 monks
1-2 mesmers (2 monks, 2 mesmers; 3 monks 1 mesmer)
1 necro
2 Warriors
1 ranger
Maybe try improving on that for a team party and attempt the tombs.
~Celestial