Sonic is a reactionary franchise. From the outset, it existed to one-up Mario, but it arrived late enough to still be a linear sidescroller like Mario Bros rather than have any sort of world map like Mario World or even Mario Bros 3. They did a racing game (Sonic Drift) two years after Mario Kart. They did a faux-3D prerendered-sprites affair (Sonic 3D Blast) two years after Donkey Kong Country. Sonic Adventure was a delayed response to Mario 64, after the quiet cancellation of Sonic X-Treme - which would have been an original and fascinating extension of tight traditional platforming, while also making children throw up. Sonic Adventure 2 and Shadow The Hedgehog are embarrassingly of-their-era. Sonic '06 took all the wrong lessons from Mario Sunshine. Sonic Lost World took half the wrong lessons from Mario Odyssey.

Sonic Fighters was admittedly independent of any Nintendo influence, but that's because it was Fighting Vipers with cash-grab characters. I think Dr. Robotnik's Mean Bean Machine is basically the same game as Wario's Woods, but I know it came out first. Sonic Spinball and Kirby In Pinball Land were chasing the same trend.

Sega's been slowly chasing trends for thirty years now, because they were an arcade company that accidentally struck gold once in the home console market, and their slow-motion crash was still a better fate than most arcade-centric developers. They're here and Midway isn't because they swallowed their pride, pulled the chute, and started porting everything to PS2 and Gamecube.