Um no, Mario didnt change one bit, he just had a very small evolution a real one at that making things better and better without changing him. While Sonic had a freaking whole character redesign which is hardly even recognizable. You look at the 90's boxart, sprites, cartoons, now that's Sonic the Hedgehog, and then you look at the "modern" look now that doesnt even look like Sonic.
Sonic doesn't have green eyes, buckles, skinny body, long legs, extra random squid spikes, and so on. This modern thing is like a fan character. Sonic was made to look and act like an American kid of the 90's.