"Hatred fueled cunning, but burned out all wisdom. Without me, you could not see."
"Strength is useless without some wisdom to guide it."
"And without him, you died. He needs your wisdom, but you need his strength. His focus."
"Each part of you was needed as much as the other. The Emperor split you apart, because you were strongest when you were together."
The quotes vary slightly, but my interpretation is that the dark side of Revan held the brute force and the light side knew how to use it. Divided, Revan was weaker, because his dark side did not effectively utilize his strength. Revan was a brilliant tactician, and while that still held true in Shadow of Revan, a big part of tactical planning is wisdom. Whether it be in a personal fight or an all out war, Revan was best when whole.
So to me, here's how it looks: Whole Force ghost Revan = Revan Reborn > Dark Revan/Light Revan.
The problem is that we never got to see Revan at his full (wholesome) power. We got glimpses of his potential. At his height, he was betrayed by Scourge. Then he was tortured for centuries and his mind fractured, which explains why he lost to the Imperial strike team at the Foundry. Afterwards, he splintered in death.
If Dark Revan could (almost) hold his own against Grand Master Satele Shan, Darth Marr, and the Hero among others all at once, then Revan Reborn should be approximately just as powerful, but with his wisdom intact.
The issue is that Revan Reborn < Vitiate, but Hero of Tython > Vitiate. We can see a direct correlation between Revan and T3-M4's initial confrontation with the Emperor, and the Hero and Teeseven's battle with him. Here's the distinction: Revan's fight was while the Emperor was in his true body. The Hero fought Vitiate while the Dark Lord was in the Voice. If it's true that a person's body, through midi-chlorian count or otherwise, can determine the level of Force power he or she possesses, then I can't help but think the Emperor would be strongest in his own body, unless he possessed someone who had more Force potential than himself. So if Revan were to switch places with the Hero for those fights, would we see the Hero fall to Vitiate and Revan succeed? I'm not sure, but I think it's worth considering.
If he doesn't have to worry about someone betraying him (story of Revan's life, right there), I'd wager Revan Reborn could beat the Hero of Tython. I think his latest and seemingly last battle proves Revan is more powerful than a lot of people wanted to believe, especially since only half of him fought. This might exasperate those who feel his character is overrated.