Last time I checked I think there is also "gameplay" in DriveClub... and better driving model too.
If by gameplay you're implying open-world layout, then there's no comparison here, if that's your preference you shouldn't even be considering DriveClub.
It really doesn't. You've forgotten what constitutes a racing game if you're declaring DC a shell for the reasons listed below.
Having more to do doesn't objectively make a racing game better. You're just entertaining the idea of sandbox game design more than strictly racing, and marking down a racer for sticking to its purpose is dismissing the foundations of the entire genre.
When it comes to driving fast cars skillfully in beautifully rendered locales, around challenging track designs, with your friends' skills literally painted onto the pavement for you to compete with, for all the bells and whistles you can put on Forza, it just doesn't hold a candle to Driveclub.
It is, in the purest sense, driving at its finest.
To call this game a shell, and soul less and bland, is insultingly ignorant.