>>39269285Pretty much yeah. This is a comparison between the XY model and the LGPE model.
It doesn seem the Sword/Shield Pikachu is the same as LGPE Pikachu. For the most part the models are very similar with just a couple polygons around the face and some edgeloops. Edgeloops can be easily added by pressing 'control T' a couple of times where you need it.
So it's safe to assume that the new HD Pokemon are just rendered from the 3D Pokemon and then tweeked a little.
As far as textures? It does appear they are making some new ones according to the texture files, but textures are not an all time consuming thing. It's why texture mods are among the most plentiful mods out there. Textures are more entry level.