So the main things, meaning the Shema and its blessings and the Amidah, are enough? Or did I not understand the Rabbi’s intention?

Indeed, on the fundamental level it’s possible (together with the morning blessings, Barukh She’amar, and Yishtabbaḥ). I thought the question was theoretical.
If you mean practical implementation, there are a few reservations:
1. When the prayer is with a minyan, it is more complicated.
2. The question is what the need for this is (how hard it is for you to pray in the usual way). There is value in preserving custom, and therefore canceling it requires a real need.

The need is emotional. God does not intervene and does not answer prayers (according to the Rabbi’s view), so prayer becomes unnecessary. Or do we simply pray because these words have to be said and that is how it was established in the period of the Men of the Great Assembly, so the feeling changes nothing and one should stick to the fixed text?

There is a misunderstanding here. The purpose of most of the prayer is not requests. That is only a small minority of it. If that is the need, there is no justification at all for changing anything (since the section of requests is part of the Amidah, which we have no authority to change). And as for intentions, one can have in mind those who need help, in the hope that perhaps the Holy One, blessed be He, will intervene and assist them. In rare cases that might happen.
I will elaborate more on this in my book (the trilogy).

Is there any expected date for the trilogy’s publication? Looking forward to it 🙂