I thought the golden age started with the PT.. And I am indeed going to say that the Golden Age means something entirely different for both.
But you have no proof to back it up.
Indeed, I could say Sidious's Galactic Empire was "the golden age of the Sith", because Sidious's Empire is, militaristically speaking, ungodly superior to Ragnos's, and Sidious controlled the galaxy, whereas Ragnos's Empire was highly limited and very, very tiny.
Who is to say which statement is more accurate? I can also say that Yoda was equal to "the greatest sith lord in history" by having a clear disadvantage the whole fight.
The NEC says he "lost". My personal opinion is that they stalemated. But the bottom line is, the term "power" in this instance is not ambiguous given the context of the situation - which was a battle to the death.
So is Yoda>Ragnos, or Kun, or Nadd, or Sadow? And is DE Luke>Ragnos, etc.. Too many technicalities.. If we talk about raw power, Ragnos would obliterate Sidious.
I do believe that Yoda is at least equal to the Ancient Sith. And, as for DE Luke, you have to understand that Sidious floored his ass in saber combat, and yet, less than a day later, he becomes skilled enough to defeat Sidious in combat?
Now before you jump on me, please let me state that the following is an opinion - but, I believe that Leia had something to do with the fight, considering how Sidious had the upper hand in the comics, and then the panel with Leia is shown (her outline is highlighted and mystical) and WHAM! Sidious is disarmed, literally.
Secondly, Sidious (still) was highly superior to Luke in the Force.
If we talk about masterminding, Sidious is the greatest ever known. If we talk about force abilities, most of what Sidious uses was derived from the ancient sith.
I don't deny that he is the greatest. In terms of achievements, he pwns all other Sith Lords.
But, then, there's also the fact that Sidious could have augmented these Force powers that "derived from the Ancient Sith".