Except they lack the aperture ring, the DA40 and DA70 do cover a full frame. Just to get that out there.
Leaving aside what people post out there - the me shots, whether 'me' is in the picture or the picture is documenting what 'me' does. I do note that in general, gauging by flickr and somewhat even places like this here forum, people respond to people pictures, to animal pictures, and to those WOW pictures that either show something new not normally seen, or that have been processed for some effect. That's pretty much it - the eyeballs are pulled in by content and not the form. I think it's always been so, only now these shots are available to all, when before they sat in a shoe box after being looked at a couple of times.
So, one hypothesis might be: only wealthy
photographers can afford the FA31, and therefore you will see mainly the
photography such people make. The wild ones can't afford such a lens
Another hypothesis might be: the lens testers are measuring things that don't matter all that much (which you pretty much say), and not just in 800 pixel portions, but even blown up as slides. The measurement microscopes (or whatever digital contraption they use nowadays to count lines) has only slight -if any- relation to the expressiveness of the images shot in the real world.
As has been said a few times already: both lenses are far better than the internet allows. Yet, through the limited internet interface, differences do show themselves.