On the Issue of the Ancient Sith, Revan, Exar Kun and Nihilus.
This topic has obviously been discussed a lot.
I'm here to offer my logical thoughts and to provide an adequate solution.
The Ancient Sith were said to be godlike, immensely powerful and so forth, due to a lack of feats and sources, we can only gauge and estimate at their power. This generally means our thoughts are subjective, our views varying and causes a never ending argument.
Characters such as Luke, DE Sidious, Yoda and etc have been given definitive feats, adequate information and so forth, essentially they have MUCH more sources/feats to name. This inherently means you can use them to prove that they are powerful in their respective times.
However when comparing a relative "unknown" and a character with a lot of sources, how do you work out a victor? Realistically you can't.
Whilst you can prove that Luke and DE Sidious can do this and do that, you cannot prove that the Ancient Sith can't, neither can anyone prove they can, the end result is that its purely opinion and subjective.
Exar Kun/Revan/Bane/Nihilus and etc. are relative to the Ancient Sith due to the fact a majority of their knowledge comes from the remnant knowledge of the Ancients, thus its is also rather hard to gauge at their power, given that they have a few more sources on them and other feats to name, it is still relatively hard to compare them to a character with books/comics/movies on them such as Sidious.
Again opinions are subjective, therefore unless something knew comes out that allows us to gauge at the Ancient Sith's power they will be relative unknowns. All that we know is that their remnant knowledge was enough to make Exar Kun immensely powerful, amplify Bane's power which essentially means their remnant knowledge was enough to make someone a Dark Lord of the Sith.
As such arguments concerning the Ancient Sith are best left alone.