What do you mean by "fully functional" ?

Genesis loads with a single mouseclick, it poses by clicking on a pose file, you can apply textures by clicking on a mat pose.

Clothing "auto converts" in a few seconds to any bodyshape you dial.

You can add bodyparts like detailed genitals or a second pair of arms or a trunk or a tail.

You can use high resolution HD morphs that make displacement maps redundant.

You pretty much can create every remotely humanoid shape you can imagine. And all textures and clothing and poses still work.

I think that's a lot more functionality than V4 brings to the table. (And BTW, V4 also has some "Studio only" functionality)

 

WHAT DOES NOT WORK IN POSER:

If you install gazillions of morph packs, then, yes, Genesis slows down. Same as V3 or V4 if you load all the morphs that are out there for them.

And if you save Genesis in a .pz3 scene file with an UV set other than the default UV's, you have to re-apply that texture/UV set again once you load that scene again.

(But there are quite easy workarounds for both problems)