Dear Avira,
The Tzadik as G-d’s Body is a kabbalistic idea with a long historical trail. Chabad did not come up with it. And it has been part and parcel to several major controversies. I’m not near qualified to decipher what is legitimate and what is heretical.
דעתי קצרה
You could use some skills on how to deal with Chabad. They can be relentless.
I can’t ascertain how much the truth matters to you. The fact that is indisputable, was that the Rebbe was quite the gaon and knew how to choose his words carefully. If the other great talmedei chachamim of his time couldn’t hold their own against him, I surely cannot win this debate outright.