For the OP:

Given the default geometry, Exnem's fix morphs, the whole set, represents the best "generic" JCM-enabled fixes for V4 limb movements.

However, that is not the case with any custom or even DAZ-distributed morphs/morph-packs. The fact is that there is no Lord of the Rings solution for customized morphs in default rigging for any wavefront.object-based figure. (There is no "One JCM to Rule Them All.")

However, the solution for this is very easy. Indeed, the solution for V4's butt, which you may not like, is very easy. In Poser, you can use the Morph Tool to morph geometry pretty much however you wish from with Poser, itself. You can save these morphs and can even create your own Joint Control Morphs or Dials in order to control them. Whenever V4 bends over, for instance, your hand-created "fix" for her butt can automagically be applied by a JCM that you, yourself, have created.

Once you get the hang of it, it's very easy to do. Whenever I am dealing with any custom sculpts for V4, I always create hand-sculpted Joint Controlled Morphs for them. It doesn't take very long and you can be as detailed, or not, as you wish with them.

So, less complaining, more Morph Tool using and learning... :) (Seriously, it's not hard. There's even a short walkthrough in the Poser manual on how to create JCMs, so you don't have any excuse for not doing it yourself.)