From what we have at the moment in the EA's story, which theme are you talking about ?
What you're willing to sacrifice for power/how much are you willing to surrender to a corrupting influence for power. Everytime you use the tadpole you surrender a bit more of yourself for re-rolls or successes, ect, you start getting dreams essentially telling you to continue using the powers, to surrender and become even stronger. Baldur's Gate I and II was about embracing your divine heritage or resisting it, though due to writing, tech, or time, it was more informed (good characters could heal minor wounds, evil ones could vampric touch for example). It was never really said, but the start of ToB (the first challenge room) the npc mentions they embraced and became consumed by the essence
Yeah, I was about to add my little 5 cents to the topic and say that the tadpole dreams are reminding me of the dreams you as the PC of BG1/2 used to have after you reached certain points in game, and furthermore - depending on what you've done (your reputation paid a factor in that, kinda flawed and rudimentary system but those games were made ages ago so they had to come up with something) you had differently flavored dreams - for good, neutral and evil reputation levels.
I haven't posted in a while on these forums, but I will remain vocal about this: we need some sorts of dreams for those of us who refuse to use tadpole powers. Give us something, we don't need a big ol pat on the back for being a 'good person', but give us something. In previous games, the 'good' aligned dreams used to have this underlying theme in them - if you didn't succumb to the corruption of your heritage, you had nightmares and general feeling of 'disappointing' the power as it tried to drown you, figuratively speaking. Now imagine getting something similar to that with the tadpole, but no, we get nothing and the tadpole is reduced to 'barely an inconvenience' as one of my favorite youtubers likes to say.
I 100% agree with the second part and the dreams/powers/else for the good playthrough.
Having played more than once as a good character, there is almost nothing related to the tadpole except a few choices to avoid. No dreams, no powers, nothing special to do... It's just completely empty.
I guess we'll have more interresting things but I don't really see any "theme" in common.
In the old games you try to learn who you are and to survive those that wants to take your power.
The Slayer will appear whatever you're doing because you loose control of your heritage.
It's only at the end of ToB that you can choose to embrace it or not.
Your heritage is what leads you to dreams, to new powers and to your journey. Your acts have an small influence on details but the stories are not really about "What you're willing to sacrifice for power/how much are you willing to surrender to a corrupting influence for power" to me...
It doesn't have any influence on the story and if there's promising mechanics that looks like in the old games in BG3 (Dreams, powers)... "A main character living with an evil thing inside him" is not really what I would call a common "theme"....
If I'm wrong I guess many films and video games have the same theme.