Team Ninja does not simply port the DOA5 character models to DOA6. There are changes to the models, some more apparent to the naked eye than others. Let's get textures and shaders out of the way:
They are mostly completely new, even on the reused costumes. The hair seems to use higher resolution and less compressed versions of textures that were created for DOA5.
Regarding the polygon models:
Here TN did a mix of reusing without improving, reusing with improving and creating new assets from scratch.
The base body models are completely new, especially on the male characters that's clearly visible. They don't just feature significantly more polygons, but they are also differently shaped/proportioned.
Faces and hair may look superficially the same, but they got a polygon boost to look even rounder.
New costumes are obviously newly modelled from scratch. Some of the reused costumes got a significant polygon boost, like Zack's muay thai gear, Rig's and Hitomi's costumes seem however to be mostly reusing the same assets of DOA5. But even there I noticed slight improvements. Rig's hoodie has a couple more polygons on the lower part of his hoodie, which now also moves during combat.
Last but not least animation and physics:
They are significantly improved on all models. One example are lower eyelids now moving, making the characters' facial expressions much more believable. They do now also smile with their eyes and not just the mouths.
So, they clearly didn't just rip the character models from DOA5 and reused them in DOA6. They completely reworked them, made bigger changes where they were necessary and smaller changes, or no changes at all, where unnecessary. That's imo a good and productive approach, no shame in that.
Also, not all completely new assets are better than the old stuff,... Leifang's new top for example is completely new, but weirdly low polygon, showing very visible polygon angles, and the new male bodies, while finally featuring highly detailed polygon meshes, look stylisticially less natural and more plastic action figure-like, and not only because of the missing navels...
I'm going to reuse this post, or at least parts of it, when the question or claim of fully ripped character models comes up again in the future.