Oh... I was referring to this:"Inside the spacious interior of the Galactic Senate chamber, Yoda challenged the Emperor. The two engaged in a spectacular duel—a contest between the most powerful practitioners of the Force’s light and dark sides."
The Complete Star Wars Encyclopedia
It does not mention of their day or of the era, so it's simply the most powerful Dark Sider in history.
Huh? That's not how it works. We don't just assume it's referring to all of history if it doesn't say "of the era". It says neither. Ambiguous. 👆
It does not mention of their day or of the era, so it's simply the most powerful Dark Sider in history. Again, there's no reason to think the Son is involved. He isn't a Force practitioner, he's more of a Force entity. Yes, he does use the Force but he's above the beings in existence due to being uber powerful and being the living embodiment of the Dark Side.
I don't think you understand how this works. The Son is a practitioner of the dark side. The quote doesn't say "most powerful dark side practitioner sans force entities". The son is a dark side practitioner, he falls under the umbrella of the quote. The quote is literally inaccurate. 👆