“Lossy” has become a characterization that doesn’t fit the new world well.
Of course it is lossy in the sense that the full rectangular dataspace of 24 bits * 192k samples cannot be folded into 24 * 44 and then restored.
Compressibility requires either that data is redundant (like PKZIP) or deemed unimportant (like MP3). (All zeros is one form of redundancy.)
MQA origami is based on an assumption of what out of the rectangular dataspace is unimportant. The belief is that this assumption is sounder than the assumptions of MP3.
So it would “data-lossy” but not “sound-lossy”.
All the arguments to show that it is data-lossy is beside the point.
The only thing that matters is sound-lossy, and that has to be evaluated. Although the reasoning appears plausible.
Some object on another basis, that compression is not useful, “I have plenty of bandwidth to download 24*352 here in my home in Switzerland.” That is not a technical judgment but a business one. And wildly out of touch with reality, in my view.