It could be that your reward comes at the end of the game when you have defeated the mind flayer tadpole in your head.
Maybe.
But in that interview the dev was going on and on about all the cool rewards you got from using your tadpole. You would think he'd also mention what you got from not using the tadpole ... unless there are no such rewards. That's why it stuck out in my mind when I read that interview.
It's the classic question of, do you bend your morality (use the tadpole) in order for quick/easy power? Or do you uphold your morality (not use the tadpole) and deal with the consequence of not having the quick/easy power?
Without the tadpole you will have to find another path to power, and I think that's fine. I can be a Fiend Pact Warlock and have access to quick/easy power by throwing my lot in with a Devil. Or I can put in the hard work and study it takes to be a Wizard. One path gets you to power faster, but the other lets you retain your morality and sense of self.
