I further suggest that not using the tadpole power is a mistake.
I think your theory is correct, and this idea is what convinced me. It totally fits with Larian's approach to things. In DOS you kept getting the source power from the gods. The powers given by the dream are similar (like many other similarities between DOS 2 and BG3 stories). I suspect in further acts characters will get more powers which also fits with Larian's habit of giving all classes magical powers. They wouldn't give you those powers and then penalize the player for using them. Its not their style.
Imagine playing through the entire game without using the Illithid believing that the Dreamer is trying to harm us, only to find ourselves then terribly outmatched and outpowered in front of the Absolute's overwhelming influence, exactly because our Dreamer is so weak and powerless.
Would be quite funny and the type of prolonged hinted switcheroo I'd expect from Larian.
At that point we wouldn't be role-playing though, they'd design an entire feature JUST around trying to trick the players. Everything we know is screaming that "tadpole = bad", and the powers are awesome, but taking away our humanity. If you play the game like that, role-playing and then in the final act "lul, j/k, the tadpole is good, you're fucked", it would make all our decisions seem completely fake, and take all control away from the player imo.
