OK so they can go into a trance? Well if they do this, then during their trance, (oh by the way all of her regular soldiers WOULD die by starvation) they won't be able to effeciently mobilze for a ambush when Revan arrives. So they'll be totally unprepared when the battle comes.
Oh yes of course, sith soldiers wouldn't even be one Malachor in the first place.
But then again, Republic soldiers would not be either - they'd go mad and run around screaming and shooting - more of a hazard really.
And we cannot forget, Traya is a wise woman. The longer Revan takes with his attack, the more time Traya has to prepare/figure out a plan (shatterpoints - very good point)
We also can't forget that Malachor basically counts as a weapon. But it is a double-edge sword - the assassins/sith cannot leave the academy.
May I add that it is my personal opinion that at least Revan could make it to the academy alive, and probably carve his way to the Core. He also made it to the academy before, so I don't think Revan would succumb to the darkside, well he might succumb, but not go mad. The dark side energies of Malachor are not that
powerful. Interesting thought, Revan would probably fall to the dark side on Malachor - is that an advantage or not?