For reasons I stated earlier: there's a difference between a loose-fitting garment that is the correct size for the wearer (i.e. it doesn't leave you exposed in the middle of the street), and one that is simply one size bigger (e.g. wearing an M when you're technically an S). The final effect is quite different. The first involves a change to only certain garment dimensions, while keeping others the same. The second is effectively just scaling up all dimensions at the same rate (that's an oversimplificiation, as grading is actually more complicated than this, but for argument's sake...).Anyway, why don't you think this answers your question? AC gave a few reasons why he fit the sizing the way he does, and why he makes the recommendations he does. I think the people posting fit pics here who go one size up look great and don't look like their clothes are too big! (I also think the people going TTS look great too).
From the post you quoted (and other comments in this thread) it is not clear to me if what is meant by "I would have basically everything we make fit approximately 1.5x larger" should be taken literally. I.e. whether A) Antonio would simply prefer to sell an M but label it as an S. Or instead, B), he'd keep the overall loose-fitting look of an M, but adapt it to fit an S in the areas of the garment that count (waist, collar size, sleeve length).
I'm guessing the answer is A). But what I don't understand is why. I'm sure Antonio has good reasons for doing things this way, it's just unclear to me what those reasons are. Other than possibly the explanation I gave earlier.