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.
So the best thing that can happen for Traya is this: stalemate. Either that, or Revan charges in with his men and slaughters the upprepared Sith. You can't be in a trance and defend yourself at the same time.
The thing is, Revan is gonna have all the time in the world, while Traya and her Sith are busy being in a trance. This gives Revan a abundance of time to plot. He wins.
This isn't gonna be some D-Day battle. It's not gonna be like storming Normandy. Revan is gonna land, have all the time in the world to plan, and either chip away Traya's forces, or just slaughter them.
Again, you are under the impression that Revan's forces are capable of fighting the Dark Side itself. Traya and her Sith can sit in the Academy all they want while Revan "plans". He can't plan for the effects of the Dark Side. There's no magic solution to protect his fellows from Malachor itself.
Troops have nightmares and discharge a blaster bolt in their skull rather than see it continue. Jedi are corrupted to the Dark Side and consumed by bloodlust, attack their allies. Even Revan will be taken into the Darkness.
Every moment on Malachor will be a living nightmare for his men. Revan can't fight the Dark Side.