I'm not seeing the graphical downgrade on Wii Fit trainer. The Switch version has higher quality hair, her skin doesn't look as washed out by the lighting, and her eyes don't look as dead as the Wii U model. Samus, the only real graphical differences I see is that she looks paler on Switch (which is most likely due to lighting difference rather than changes to the character model), and that her suit is less shiny, which seems like an improvement to me. As for Snake, there does seem to be an actual downgrade there, which is strange considering how much more powerful Switch is than Wii, his gun texture is awful on Switch, and his elbow pads look lower quality as well.
Now artistically of course I see big differences. Samus and Wii Fit Trainer have smaller boobs, while Snake has a flat "Hank Hill" ass. Seeing as I'm not gay, I couldn't care less about the Snake change. The smaller boobs are actually an upgrade for me, as I prefer smaller chested women. Samus in particular was too big before, now she is just right, super hot. If they keep her like that she may become one of my mains alongside Sonic and Greninja.