I just don't see it being a clone. Yes it's of the same subgenre but I think there are more differences than similarities if we're looking at them both as Kart racers.
The physics based racing means the karts control differently (which has been a sore point in some reviews so I guess they should have just copied Mario Kart)
It has systems for rewarding good driving that allow you to block incoming attacks (putting up a shield) as well as boosting like in Burnout
You can upgrade weapons by holding on to them and getting higher levels
It isn't a kart racer designed to be in the "Sony Universe" and only has a few Sony characters as preorder DLC
It has an actual story mode beyond "race in the cups and stand on a platform at the end"
And of course the elephant in the room, the massive amount of customization that is in no way possible on any Mario Kart ever.
I agree that 3DDGH is a clone of the old 2D Zeldas, but if you think MNR is a Mario Kart clone I think you have too liberal a definition of the term.
...
