>>11810261Sonic is really just an amalgamation of animation influences. Speed Gonzalez and Tom and Jerry give him the speedy rodent trope. Bugs Bunny gives him his personality. And Goku gives him his superpowers. A lot of Japanese mascot media has western cartoon influence but I always liked how with Sonic the balance seemed a bit more prominent.
I think the reason why the eyes are "like that" is tied to this. Being able to get that level of animation like expressiveness out of a 64x64 character in the classic era required serious exaggeration, while Mario comparatively has a more complex design but kind of had the expressiveness of a deer.
Notice all new Sonic characters started getting clothes when they jumped to 3D. They had more room for character design. Although Amy was an earlier example I suppose.