Not sure if you misunderstood the issue. But if you take two people of same height and general shape and look at just their skeletons they will be indistinguishable, yes. But skeletons do not make characters. Its the skin, the hair, the face, the outfit, the expression, the small imperfections and asymmetries that really nuances and makes the individual unique. Saying that just because a character has the same skeleton as an other invalidates the concept of that second character is probably not what you meant ... right?
About the technical limitations of importing animated custom 3rd party character models into the game, it simply doesnt through the custom mesh importer because that plug-in doesnt support skinned mesh objects, only static models.
The thing is, for the usual animations, that works, but even as is right now in Wild Life, some parts of animations are modeled around customisation and it shows as far as I remember.
Best example I can give are boobs. They act the same for a specific skeleton but that makes them flat on some skeletons (like if you max out Maya's slider they're flat, if you set it very low they're pointy)
Butts are the same. I think there isn't a single scene in the game where the butt is actually touched...and for good reason, the interaction would clip through or float the moment the butt size is modified...unless there's some point where butt skin will always stretch to no matter the butt size, which can then break the shape of the butt and yadayadayada
Idk why the hell I refered to skeletons in that last reply, but what I really meant to say was that two characters that are even marginaly different can't have the same animations without some touchy parts of the animations being floaty or clippy...so the detailed animations look bad with custom models regardless if the skeleton is the same or not.
The simple animations are mostly unaffected most of the time though, as long as the important parts (main joints, head, crotch position) are all in the same place, which as far as I'm aware are what defines a skeleton.
But obviously if not even the skeleton is the same then the whole animation doesn't work.
Not that there's any better way of doing this, really, I'm glad there are shared skeletons in the game but at the same time I feel that, fixed, non-customisable characters would make for animations that are much more touchy and muuuuch better overall...it's a tradeoff in the end.