Yuji Naka really fell off hard after Sonic Adventure 2 and commercial failures of Sega's hardware endeavors as a whole. Went from being Sega's golden child, to being arrested for securities fraud.
Allegedly he was extremely difficult to work with and would not share the Night's 3d game engine with an American team that was developing a 3d Sonic game for the Sega Saturn, effectively kneecapping a big part of that console's commercial viability
Sonic Adventure 1 is infamous for its lighting/textures successively degrading after each port from Dreamcast -> GameCube -> PC. There's a famous video showcasing all the changes: https://www.youtube.com/watch?v=SORYL5J1Heg
Allegedly he was extremely difficult to work with and would not share the Night's 3d game engine with an American team that was developing a 3d Sonic game for the Sega Saturn, effectively kneecapping a big part of that console's commercial viability