You are just saying that cause you are too blinded in your anger to even agree with others.. You are more one of those people that wants to be "Always Right" and will constantly argue with everyone until they submit and say "Fine, you are right."
That is why my theory makes no sense to you.
No, your theory makes no sense to me
because it's needlessly complicated and Occam's [censored] Razor.What is the likelihood that the devs discussed and made a concious decision to implement a retcon BUT also decided never to address or acknowledge that retcon and cover their tracks by providing the players with an explanation of why Immortal Blood is fiction? Very slim, as doing so is both very odd and risks annoying lore masters who fail to make sense of the retcon. It's sloppy and frustrates fans, and thus is not a wise decision. If they covered their tracks at least, THEN your theory makes sense, but they didn't...
What is the likelihood that the "Volkihar" we see in the base game are so similar to the Oblivion strain simply because the devs couldn't be bothered to make the vampires lore-friendly? Pretty high. I mean ffs, half the faction quests feel unfinished too.
The likelihood that my argument is correct is far more likely than yours. I can name a number of criteria for why your theory is very unlikely (two examples above) whereas you cannot name criteria for my theory.
The fact that they failed to cover their tracks and give a good explanation as to why Immortal Blood is fiction? That wreaks of laziness, NOT of your theory of it being a concious decision. If they sat down and had the discussion and opted for this retcon, they'd probably prepare an explanation for it. If they didn't have such conversation, then they wouldn't prepare anything and just do whatever (Underworld vamps) and then there's no natrual transition.
The simplest theory is often times the correct theory. Yours is, by far, not the simplest. Dev apathy or laziness? Now
THAT'S likely.