The Gra גר''א [the Geon from Villna] also thought that Pantheism was something that some Jewish cults got from other sources and not from the Torah and were trying to convince people that it is a Torah principle.
The problem here are far as I see it is that some people are not accountable to any external validation. They can define things and conceptions as Torah concepts as much as they like with no worry if Torah or reality agrees with them. The main thing is that other lunatics should agree with them.
Nor do they need to worry if logical reasoning agrees with them. [At least some philosophers before the twentieth century used to be concerned if their conclusions could be supported by logical deduction. ]
What the Rambam [Maimonides] tells us in the Guide for the Perplexed is that the belief system of the Torah is Monotheism. This really was clarified by Saadia Geon in his book Emunot VeDeot but the Rambam spends much more time explaining this in his book.
The Hindu system is Pantheism, and if people want to be Hindu, then that is their option. But it is not an option to lie to people about the belief system of the Torah.