This gets cited here weekly, usually second-hand, so it is worth setting out what it does and does not establish.
There is also a quality change that the scan cannot see. Weight loss shifts fiber-type distribution toward Type I and improves mitochondrial density and insulin-stimulated glucose uptake per fiber — so the muscle you keep is metabolically better even though there is less of it. That does not make the loss irrelevant, but it explains why function often holds up better than the number suggests.
Where I think it is weakest: the subgroup findings are the part I trust least — with enough subgroups something is always significant, and these were not all pre-registered.
So the question, as narrowly as I can put it: what fraction of loss being lean mass is actually normal, because the numbers quoted here range from 10% to 40% and cannot all be right. I would rather have one careful answer than five confident ones.
Note on sourcing:
Figures above are from the primary publication rather than the press summary. If a number here disagrees with one you have, post yours and we will work out which of us is reading a secondary source.