I entirely disagree. The powers from the tadpole, are a direct homage to the powers from Bhaalspawn. An evil entity using you(Bhaal), a new god The Absolute(Rebirth of Bhaal using his spawn as a new vessel or just taking over the throne), Having to give into the influence of the tadpole, or resist it(literally exactly what you are doing in BG I), the true souls are working together(OK so not this one, Bhaalspawn were more of a Highlander, there can be only one, getting more powerful from killing your half-siblings. However, we do see that....forgot her name, The Goblin Shaman seems to be a true soul and wants to study/kill you, so maybe it will be Highlanderesk in the later chapters.) Then who is this Absolute, its a new god, and its definitely not a benevolent one. Could this be the Bhaalspawn that ascended?
As of right now the game seems like a love-letter to Baldur's Gate I & II. It's also EA, and I'm sure they want to leave some big reveals to come as well.
Interesting points you raise here about the tadpole powers and to some extent I agree but at present it is are just a theory of yours, not a fact and from my point of view I don't see the homage or love letter to the original BG games in any meaningful sense. The Bhaalspawn powers in BG2 if I remember rightly were not introduced until some way into the game (could be wrong here I admit). Maybe The Absolute is as your theory suggests but story aside, when I think of homage I can think of plenty of other things that have no link to previous BG games.
By implementing so many things that were in DOS: no day/night cycle, party chain mechanics, 4 person party, explosive surfaces, healing food, etc., it's inevitable some people feel the lack of familiarity. Clearly nobody expects a replica of a 20 year old game but I find the soul of BG is indeed missing in BG3. I understand some people will disagree with me and that is fine; these are all just opinions after all.
I read in another thread that someone described BG3 as having a feel similar to a Marvel film and that resonated with me, from a story/companions/overall tone perspective. From the crazy intro hurtling through the planes to the exceptional backstories of the majority of the companions, everything feels very extreme.