2020 has way better composition and clarity, it's much more readable.
2008 version has a bigger emphasis on realistic shading, sure, but Dhalsim doesn't even look like he's facing Blanka. It looks like he's reaching for something behind him. The perspective is just a bit awkward and it definitely seemed to have bothered him seeing as he had gone out of his way to completely redraw Blanka.
Also the foreshortening on Dhalism's arm and hand is a bit wonky in the original, which the 2020 version fixed.
The heavy stylization in the updated version looks very much like a design choice, probably to reflect his current artistic output. I'm sure if he wanted to do realistic shading he could, I doubt he just "unlearnt" how to do it.
Overall, the 2020 version showcases better draftsmanship skills and overall technical ability, but I get if it people prefer the original regardless.