Easy. By not training Revan. What could a Revan without a lightsaber/s and force powers do to the Jedi Council, or any Jedi Knight?
One on one, perhaps not. But if you had Atris, Vrook, Zez-Kai Ell, Kavar, Dorak, Zhar, Vandar and Vash all against Revan at once, there's no way in hell Revan would win. Yes, Revan is powerful, but VERY OVERHYPED!
A master or two? Nihilus wiped out a whole planet of Jedi, including several masters. I will not get into this whole annoying debate again, but to put simply, given Nihilus' void in the force, planet eating, inhuman, no will of his own status, only the Exile, a wound in the force, could beat Nihilus. NO ONE ELSE could. And no, it does not mean that the Exile is more powerful than Revan.
Prepare the Republic by attacking them and weakening them? I don't think so. Revan may have started out with 'good intentions', but it is folly to argue that Revan never 'truly' fell.
I think you um, missed something? Revan was not powerless when he was captured, unarmed perhaps and unconsious, but probably more than a match for one master. Many of the masters probably feared that Revan would escape their grip, as charismatic as he was, and somehow manage to get back as the Dark Lord of the Sith, with or without their help. Ponder also over what Revan could've been able to do to the Order (as vulnerable as it was). And if we know Revan's charachter, he would've probably refrained from confronting the council at the point of his capture. He probably would've waited for a moment where the masters would relax and slip up enough for him to Return to power in some way. (Don't ask me how lol) Revan's a strateigst, he does nothing when there's nothing to be gained for the higher cause. Maybe a leftover way of thinking from his First Master?
I agree that Revan hardly could've stood against all the masters, maybe he'd take a few down with him, but in the end the Jedi would've overwhelmed him - though I doubt the whole council was gathered at the point of his capture. But that we know nothing of.
Also saying that Nihilus wiped out an entire planet and all that. Sure I admit that Nihilus was powerful. But do note that Nihilus never engaged any master in hand-to-hand combat and therefor the masters never truly got a chance to prove themselves against him, nor did they expect his arrival.