I am a big Revan fan. He is awesome -- and that is partly because he is not overpowered.
It's like Superman. A character is pretty boring if he can't be beaten, if you don't fear for him. Revan is a bad***, but he isn't unbeatable.
I agree with OP. Revan could duel all these bigshots for a bit. That is my opinion. It is also my opinion that he doesn't have a huge chance of beating them. It isn't a set-in-stone thing, however; everyone makes mistakes, everyone gets distracted. And at the level these guys are at, one distraction can be the end of a fight. Look at how Palpatine -- the Super Sith -- went down. He didn't see Vader coming. So just because one character is more powerful with the Force -- whether that "power" is measured in knowledge or raw strength -- or is a better duelist, that doesn't mean they win 100% of the time. Just a little something to keep in mind.
Setting aside for the moment the tricky issue of whether or not Revan's "Force Balancing/Juggling" is canon, you need to look at whether balance is all that great in a fight, a single fight. Being "balanced," it is unlikely that Revan could hope to match Palpatine or Luke in any Force duels. Revan is said to be skilled in a variety of diverse Force techniques -- meaning lightning AND healing, which I consider diverse when they're found in the grasp of a single individual -- but, to my knowledge, isn't said to have mastered any of them (I could be wrong there, though). So Sidious could "out-lightning" him, because Revan likely hasn't focused nearly as much on his Force lightning skills as Sidious has.
In regards to Ki-Adi-Mundi beating Revan -- I must say I'm skeptical. Yes, Ki-Adi-Mundi is a powerful member of what is said to be one of the greatest Jedi Councils of all time, but Revan went up against Darth Malak when Malak had the power of the Star Forge behind him, and won. Revan went up against (spoiler for the Revan novel and at least one TOR class story)
So I'm not so certain Ki-Adi-Mundi, great Jedi though he is, could reliably be said to have a good chance of beating Revan.
As said before, Revan wasn't at his prime when he appeared on the Foundry, and from what I've seen, most of the Versus threads state that participants are considered to be at their very best at the moment of the fight. Plus (WARNING: OPINION AHEAD), I think the fight between the Four Speeder-Bikers of the Empire and Reborn Revan is waaaaaay too complicated to draw much from. There is no CANON "choreography," if you will, of how that fight went down. Some of the Four Speeder-Bikers could have ended up in kolto tanks from that bout; the Agent could have sniped Revan in the face while he was monologueing; we don't know. All we know about that, is that somehow, the Four Speeder-Bikers won.
Let me address the Kreia thing...
Here's how I see it. Kreia adored Revan. Kreia saw big things for the Exile. Kreia lied so much that is impossible to say, "Kreia said so, so that's PROOF!" Yes, at the end of her life, Kreia made some predictions. That she wasn't wrong about those predictions is not proof that she didn't lie about the other stuff she said at that time, defeated or no. It is possible to lie in one breath and tell the truth in the next
In regards to a Revan vs. Malgus (or Satele/other NPC of the time) match-up:
Malgus is a beast. I don't know nearly as much about him as I'd like. But I DO know Revan rather well, and I'd say Malgus is the underdog in this fight, because, let's face it, Malgus is not and never was a PC
All kidding aside, I'm thinking Revan has as good a chance of beating Malgus as Malgus has of beating him. Revan is a good enough lightsaber duelist that he can hold his own against an opponent long enough for SOMETHING to happen that would either distract him or distract Malgus. Same with Force abilities and general fortitude. I think whoever wavered first would lose, as they are both skilled enough to take advantage of any openings. My opinion, not too many facts, so take it or leave it
(As far as PC vs Revan battles go, at the end of Act III, I'd give it to Revan; but remember, the PCs are not yet at their prime.)
Revan good. Revan bad. Revan beast. But Revan no Luke-level, and that a GOOD thing.
Sorry for the walls of text