Since some people think that Ken Sugimori still does all the artwork. I made this thingy to show the differences.

Pay close attention to how the lines, shadows, and highlights are done for each one.

Ken Sugimori hasn't been doing all of the artwork since Gen 7. Gen 7 is when Ohmura did a vast majority of the art for the new 'Mons, while Sugimori did the art for the Alolan Forms and new mons/forms in USUM/LGPE

In Gen 8, all three did artwork for mons. (Look closely)