Incorrect. The Receptor has major vents that work really well: http://www.pocsports.com/en/product/1229/receptor-backcountry-mips They are covered to prevent penetration, a two-level design. Pretty sure they can be opened and closed. The Receptor runs large; I am a XL in the Comp and a L in the Receptor, can get into my son's M without too much strain. Also a slightly different shape than the rest, bit better for oval heads.
Can't speak to "much heavier," since have not tried on a Fornix, but the Receptor's a pretty light helmet. As light or lighter than the Skull X Light. My son is 7, for instance, and doesn't have the thickest neck. He hasn't complained.
Not clear what "microsize adjustment" means; all POCS come with extra pads to put in, and usually have a set inside that can be removed at will. Far as I know, some - new Skull II, Fornix, the kids helmets like the Bugs, have a band in back that can be tightened or loosened. Not sure that's necessarily a good thing, incidentally, since it could produce a space at the back between your head and the helmet where shock absorption is being handled by a plastic band. But I'm sure POC engineers have that thought through.
I've owned the Skull Light with the little goggle vent in front and have never noticed a difference between its performance and the Comp's, without a vent. OTOH, I can feel the difference between either of those and the helmets with top vents.
One thing that never comes up in a discussion of vents, incidentally, is trees. Around which I would not want unshielded vents. Or prolly vents at all. Ever had a low branch hook onto your helmet or goggles? Not a pleasant experience; IME the smoother surface brushing branches the better. Ditto for running into rocks, I'd guess.