To be fair, probably not a lot of people willing to personally setup or find a modlist that combines the NSFW and gameplay, so the visual aspect is the only thing they'll really be comparing. Even then there's guaranteed degrees of jank in Skyrim but nothing really compares to the sum of its parts, let alone individual aspects like NSFW content variety or even SFW character creation. Especially when WL as an example just doesn't have much gameplay yet, NSFW or otherwise.
I just think these comparisons are self-defeating anyways since Skyrim is a decade old RPG and WL to-date is more of a NSFW animation sandbox - ofc there will have been advancements in animations, rigging, VFX, etc lmfao.
I've never been into NSFW gameplay mods, I'm friends with ppl that are and I'm still amazed by the experiences they come up with. I am a big fan of character creation and that's very limited in WL since it's all preset chars with preset options, scale-based slider morphs rather than geometry morphs, the skeletal limitations you mention, and some really important details like a lack of control over expressions in the animation itself since they're all premade and baked into the corresponding animation's runtime(which looks funny when you speed it up lol)
Sorry about the rambling but this is an interesting topic, it is confusing to see a dude demean the work put into Skyrim modding, for something so contrived as "this 10 yo RPG's NSFW mods don't compare 1:1 to a bespoke NSFW render on a cutting edge engine" xD. The grass is always greener on the other side as they say!