Damn_Underscore posted...
The closest Sonic 06 is to being Sonic Adventure 3 is possibly, when they were first making the game they intended for it to be Sonic Adventure 3. But soon into development they realized how bad and totally undeserving of the Sonic Adventure title it was, so they gave it the "placeholder" name Sonic the Hedgehog. But of course they never changed that name either.
The game just needed time to work out kinks for improvement. It was named Sonic the Hedgehog because it was rebooting the series