The base mesh is a bit different but pretty similar.  It's provided in low-poly only, and is dynamically subdivided within D|S.  That's another problem with DAZ providing a Poser-ized version, because Poser doesn't currently have that feature.  Some of the differences are e.g. the fingernails and toenails are welded onto the base mesh, whereas with V4 they were separate geometry.

The UV map is almost exactly the same, so you can share textures between the two.  That's a pretty good thing, imo.

There are some interesting features to Genesis besides just the rigging, but they're specific to DAZ|Studio and not so much the figure, e.g. "Smart Content" (no more "Update V4/M4", no more morph channel micromanagement) and ability to give you an alternate UV map if desired.

Deciding to redo and release the old V4 morphs was probably a combination between it being a pretty easy conversion (I'm almost certain the conversions were done by automation, something like what Morphing Clothes does) and to reassure buyers that they'd be able to obtain familiar looks that they liked with V4.

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