that's not even close to the same thing. We were explicitly TOLD there WAS a Dominion War, so it's assumed there were parts of it we didn't see.
And we are expressly told that the Federation had encounters and information about the Borg before Q Who as well.
As evidence, I present Regeneration, the El-Aurian refugees rescued by the Enterprise B and the line in Voyager when they mention the USS Tombaugh.
Well, I gave you your evidence just above.
And since we know for a fact that the Federation knew about the Borg, and since we know for a fact that Picard didn't know about the Borg until Q Who, doesn't that indicate something there?
adding on from stuff we're told is totally different from making up explanations yourself.
In both cases, aren't we looking at what we are told on screen and extending that information in the most logical direction?