User content will never be as polished as developer-created content, but that doesn't mean it's not a worthwhile pursuit, especially in a long-running series like this, and ESPECIALLY when Nintendo has been taking more criticism lately for not changing up their games enough (A Link Between Worlds notwithstanding). Plus, I don't get what graphical fidelity has to do with the inclusion of a track editor?
Hell, in an even broader sense, Nintendo has been having trouble justifying their Gamepad, and this would have been the PERFECT opportunity. It would have made editing a lot easier either through better selection of components for the track or even another vantage point for creating sections (solving the anti-grav thing, which I don't think would have been a problem anyway). Yeah, it might have been hard, but I think it would have been something worth doing. I'll add it to the list of things that is in Smash Bros but not Mario Kart for some reason