Koopa Drift is so much fun to use lol.
I know it sounds gimmicky, but I do think we should try to explore it more and approach it differently.
Instead of being used for comboing, we should be using it to mess up our opponent's neutral.
It's great for messing with an opponent's positioning. If you hit them they get carried with you until you stop, and that usually ends up putting them offstage, ripe for an edgeguard. Because of Koopa Drift, Jr, can go SUPER far for an edgeguard and almost guarantee his recovery while the opponent may not. You can still jump cancel it for a bit of height too.
If you adjust the timing of your spinout from a midair kart dash, you can also propel yourself upwards a little bit above the ground while spinning out. This is how his horizontal recovery becomes so good, and it should catch opponents who try to short hop aerial, or at least provide a little more protection than if you did this on the ground.
I know this is sorta theorycraft, but I think it's worth testing.
I'm going to try some more serious matches on Anther's ladder to see if Koopa Drift really is just a gimmick or not.