I think that the Dark Urge originated from the tadpole thing. The more you used its powers, the less control you'd have over your actions, and ultimately, you'd transform. Now, with the DU origin, that'd make these elements overlap. Instead they went with the "tadpole tree" instead.
Personally, I'd have preferred the former version. You could play evil, use the tadpole and become more and more erratic, barely clinging to your sanity at some point.
For the custom origin, I'd have done a different story altogether. Maybe not even an absolute evil one, maybe an antihero arc with a chance of redemption.
But it is what it is, and I still don't use the tadpoles.
No. Without going into spoilers the Dark Urge has nothing to do with the tadpoles and it never did. Also based on datamined info it seems like the Dark Urge was originally intended to be the base Tav experience regardless of tadpole use. It's more related to the plot of BG1 and BG2 than tadpoles. That's why it seems like like the Dark Urge is literally Tav+ or rather why Tav seems so bland and empty.
