Absolutely amazing work !

As usual, many ways lead to Rome, but some are shorter than others.

Up to Poser 7 morphs were seriously handicapped because Poser read joint deformations first.
So people added more bodyparts to spread deformations more evenly:
First buttocks, then a waist  and then double jointed shoulders.

But a joint deformes the mesh according to a spheric influence field while a morph can allocate a new position to every single vertex of a bodypart.
So the information density in a morph is a lot higher that in a joint deformation, that's why a morph can give you a much more exact shape.

Additional bodyparts also make manual posing and cloth creation harder while a figures' joint fixing morphs can be simply ignored in loose fitting cloth and for tight fitting clothes easily re-added with the morphbrush.

A couple of joint fix morphs really also don't add much overhead either, as the majority of figures the head mesh uses about half of a figure's entire mesh, so by far the most RAM is used up for face/expression morphs.

But again, as I said before, it doesn't hurt to make the mesh bend as good as possible by itself before you bring in the morphbrush.
The less "fix" is necessary, the better.
So if you can get rid of that seam and make that buttock work properly, I'm all for it.

But avoid getting carried away with extra bones like teeth or tounges as these are a pain to adjust if you do some serious morphing or even swap heads with another mesh.
And please no multiple ERC functions with null body actors, morphforms or scaling poses or whatever.
I never liked the "sight of line" thingy of Apollo either as it added extra complexity and looked goofy in preview mode.
MIKI's eye controls that move both eyes simultanously are a great improvement, though.
V4 again carried ERC control way too far with all her faux-expression morphs.

The simpler you keep everything, the more other people will be able to use it.