XSUPREMEXSKILLZ
The Immortal Emperor
I completely agree that it strains credulity to think that all three sources are wrong, but that's what happens when you have so many authors writing a character: contradictions occur. Explicit evidence from actual fights Vader partakes in (the vast, vast majority, if not ALL of them circa 19-17 BBY,) don't paint Vader as a worldbeater by any stretch of the imagination.
This type of thing happens in comics all the time as well: one or more authors will paint Galactus ass a multiversal threat through statements (and even sometimes feats,) but the vast, vast majority of authors and statements put him at universal. Which one do you choose? IMO, the more consistent one.
1. Sure, but via showings, he lacks the ability to tap into that raw power to such an extent that he struggles with random nobodies 9.9 times out of 10.
2. Sure, but you'd have to show an inconsistency in terms of feats for Vader circa 19-17 BBY, because from where I'm standing, they're consistently "bad" (relatively speaking).
That's the thing...What exactly is high-end early Vader? We've seen it with Luke, but I don't think there's been much fluctuation in terms of Vader being "shit" or "not shit."