Okay, so I’ll ask more specifically—do you accept his approach regarding prayer, that one prays because “that’s what one is supposed to do,” without any intention at all? And his approach, which he developed from the words of Meshekh Chokhmah, that there is no holiness in anything created or in objects?

Regarding prayer, I suggest you search the site. I’ve elaborated on this in quite a few places. In brief, I accept his approach as a foundation (that the basis of prayer lies in the declaration that there is an obligation to say it), on top of which come the usual layers of prayer. This approach of his is a good example of a general characteristic of his: he takes a correct idea and goes much too far with it.
Regarding holiness, I really do not agree. In my opinion, even Meshekh Chokhmah did not mean that. The matter is explicit in several places, that there is holiness in the object itself and not only in the person. In fact, the concept of holiness is the main concept for illustrating a law that applies to the object itself.

By the way, Meshekh Chokhmah himself wrote explicitly in several places not in line with the things Leibowitz attributed to him, but Leibowitz selectively chose the passage that can be interpreted in accordance with his own view (as he also did with Maimonides).