No Aperture on the Q??
Dude the ND filter isn't fixed, it switches in and out as needed. So no advantage at all of "bringing your own".
The idea is that a ND filter is preferable to really small apertures, as this avoids diffraction artifacts and, probably more importantly for a consumer ILC, unsightly dust spots.
The Ricoh GR digital did the same thing. In practice you never noticed it. I believe aperture settings above F9 on that camera were "virtual".