adhoc,
Sorry for the delay. I am not on the forums much on the weekends.
To answer your questions:
1. I think the perception of sharpness is just that, a perception. The Questa does not have great depth of focus (not to be confused with depth of field). This means you are either perfectly on focus or you are completely off focus with the slightest tap of the focusing knob. I can see how this short depth of focus could lead some folks to the perception that they are not sharp. Second, I think the slightly warmer tone can also contribute to this. I find that colder biased or neutral image representation gives me the impression of increased apparent sharpness. I would assume that a warm bias does just the opposite. In actual side by side comparisons though I was able to detect no difference in apparent sharpness between the Questa and other comparable models.
2. The two pluses, for me personally, for the Questa over the two other models you mentioned are the eyecup design and the rubber armoring. The eyecup diameter of the Questa is narrower than the other two which contributes to easier IPD/eye placement and subsequently a more immersive experience (which is of course highlighted by the wide field of view for an 8x42, excellent edge sharpness/large sweet spot and very good CA control).
The rubber armoring on this is a very basic, contoured, tactile-friendly design. It feels very good to put my hands around and the thumb indents very smooth to put my thumbs into. "Like a glove" if you prefer.
3. No, I didn't run into any AMD issues because of the field flatteners. I thought it was well balanced with pincushion distortion in this model.
4. Yes, I still have it and I will say that I have used it more than any other bin I have at any given time.
The only negative, as I mentioned in my original review, is that it is a bit hefty but that is the price you pay for a full-sized field flattener binocular with a wide field of view. The only way to somewhat avoid this is by producing an 8x32 model of this design which, of course, hasn't happened.