XSUPREMEXSKILLZ
The Immortal Emperor
In regards to the thread, this is how I see it:
"Even in his weakened state you are no match for him."
"You’ve learned that the Emperor is on Dromund Kaas, temporarily weakened by your efforts thwarting his plan for galactic annihilation. Striking at him now is your best chance to defeat him once and for all."
These two quotes reinforce the fact that-yes, the Emperor was indeed weakened. Although the extent of his weakness is unknown, it's safe to say he wasn't weakened only slightly, considering the magnitude of the ritual he was performing. It's only logical to assume that since the ritual was one of galaxy-destroying power, having it backfire would weaken the Emperor quite immensely. Now of course, that's only the onset. The Emperor's been recovering for hours in the dark temple, though how much and how fast it would replenish him is unknown.
The Hero, similarly, would probably not be at his peak power either. Not only does he have to fight through the Imperial Guard, "the ultimate non force sensitive warriors in the Empire," but he's doing so through the dark temple, a very powerful concentration of dark side energy.
Something people consistently bring up is that if the Hero is light side, he goes to save his apprentice before confronting the Emperor, along with the Emperor's confirmation that he has, "dissipated their energy saving the weak." This is merely a demoralizing statement on the Emperor's part, as if you choose to not save your apprentice, the Emperor says, "you have gained little." And to add a bit of logic, if the Emperor's been recovering for multiple hours, a few minutes wouldn't make him exorbitantly more powerful.
In regards to how this makes him more impressive than Revan, allow me to explain.
-The Vitiate that Revan fought was inherently weaker than the Emperor in SWTOR, as the Emperor is stated to have, "ever increasing," power, plus he's been siphoning energy from Revan and the Emperor's hands, along with other individuals across the galaxy.
-The Hero and the Emperor were in somewhat similar conditions.
-Scourge's revelations in SWTOR heavily imply it, stating that Revan and the Exile, "didn't have the strength to complete their task," and this:
"Jedi, shining with the force, were lined up to destroy him. All were swept aside. Revan and the Exile were cast at my feet. Then, out of the shadows, one jedi emerged to cut the Emperor down. That jedi wore your face."
-Scourge to the HoT