3. Using the tadpole: The Emperor used the tadpole to communicate with Tav. Just like Tav used the tadpole to communicate with Lae'zel and Shadowheart and so on. The Emperor keeps you from being turned into a mindflayer. The Emperor helps you unlock the power of the tadpole. But the power is still coming from the tadpole.
4. The tadpole changes you: Yes, it does. In the Emperor's opinion, it changes you for the better. The Emperor being the dream persona doesn't mean the tadpole doesn't exist or grow or change the character or give mental powers.
5. Letting her in: The Emperor does not want you to resist. The Emperor is asking you to let him in, to listen to him, and the Emperor is attempting to manipulate you with a persona drawn from your own imagination. "Let me in," the Emperor says. Why is that hard to understand, but it's easy for you to imagine the tadpole saying, "Let me in."?
6. Destruction of Baldur's Gate: that scene was not entirely clear in early access. You saw a ruined city on fire and the dream persona claimed you would have what you want. Perhaps some people wanted to ruin the city, to be a warlord. That was certainly Shadowheart's interpretation. But maybe it was a vision of the future and maybe what you wanted was the ability to stop it or save the city. The point is, the scene was basically showing the stakes of what was to come. With the power you would be able to defeat your enemies.
That you can communicate with other infected using the tadpole is what Nettie tells you is unusual about the situation, and not what they expected. Mind flayers can communicate telepathically and as you can see in the example of Bluurg and Omeluum (and in the full game emperor's criminal enterprise) they don't need to use tadpoles for that. I think this is standard mind flayer lore, that they are a telepathic species. And if Daisy was the emperor, then it is not explained why in the EA he could not communicate with the protagonist at all until you progressed enough with the tadpole powers.
Because Daisy did not even 'see' you character, until you start using the tadpole powers. The very first usage resulted in just hearing their voice asking 'where are you?'. And only once you start on the possible transformation path, does Daisy show up your dreams. This is consistent with elder brain lore in the game and how they can sense and control illithids in a wide radius around them. Omeluum's ring in the EA used to prevent Daisy from reaching you, but it did not prevent you from further communication with him.
As for the vision of the city being destroyed, in that scene the protagonist is and Daisy are holding hands. Daisy tells you "the world will bow". This to me doesn't seem like a warning from someone who wants to prevent the city destruction, so that they can keep their criminal empire. In the full game the guardian instead talks about fighting the absolute and saving the sword coast, which is in my opinion is a change made to accomodate the emperor's own goals.
