Lovely 5396G - (real watch p0rn) Great to see it!
I support this decision!
Regarding the size of the moonphase aperture: it does not seem small to me. The numbers on the date ring are slightly small and they flip when you go to the "southern hemisphere" around the dial--kinda sucks that 9 is the first number at 3oclock to do that as it could be confused for a 6 but I agree w the decision. If that approach bothers you then note GP did it the opposite way.
One of the biggest reasons I waited to see it in person before I bought it was this: I think the balance on the JLC Master Ultra Thin (the 40mm one that looks exactly like the MUT MP but with a small seconds dial at 6pm) is off. To my eye, the case is too large for the size of the second hand dial. Either reduce the case size or increase the small seconds dial. Fortunately for me, the proportions are spot on for the MUT Moon (to me). I don't know if you had the same concern, but I thought I'd throw it out there.
Both are beautiful watches. In the final analysis, I think it really comes down to simplicity v complication.