It terms of overall core gameplay, and in terms of creative direction, we can absolutely split "modern Sonic" broadly into at least two distinct sections. Unleashed provided the gameplay template for Colors, Generations, Forces, and to a certain extent it appears Frontiers. Heroes, Shadow, and 06 may not have been called "Sonic Adventure 3, 4, and 5" respectively, but at their core their gameplay is still basically more of the Sonic/Shadow gameplay from the Adventure duology. The "Adventure and Adventure-derivative games" more often than not had Iizuka as either Lead Game Designer or Director (06 being an exception) and they tend to focus on 3D platforming gameplay, while the "Unleashed and Unleashed derivative games" more often than not had Sumitomo in that position (Unleashed and Generations being exceptions) and tend to focus on behind-the-back-running-forward (what I'd personally just call "racing") gameplay. This latter type even aptly characterizes Secret Rings, which did the faux-racing gameplay before Unleashed (so we could almost say "Secret Rings and Secret Rings-derivative" instead of Unleashed). 06 is certainly a transitional game in this regard, as its mach speed sections come across (to me at least) like they formed the foundation of Secret Rings' gameplay (which began as a Wii port of 06). Pinball Platforming, 3D Platforming, and Racing-Platforming mechanically characterize the three distinct "eras", and Yasuhara, Iizuka, and Sumitomo creatively characterize them. Which, since we're talking about games here, using the genre or the game-designer as the descriptor, rather than the writing, seems more apt to me. This only works very broadly, but broadly it does indeed work, I think.