I see nothing wrong with wanting to learn how to use your edges before learning how to overcome them.
Long skinny skis accentuate the edge effect. They are the opposite of a multi-directional smearing tool.
The only thing I would advise against is learning to ski powder with skis that are too stiff. Skis work a lot better in powder when they can bend into a curve.
Of course, there is the alternative of spending most of your time on fat skis, which let's your carving skills lag behind your other skills. Over the years, especially since the advent of fat skis, I've seen some excellent smearing off-piste skiers who's carving abilities had significant room for improvement.
I would advise that you ski side country on skinny skis and rent fatties when you go out with friends on a powder day, unless you can afford the extra skis for the quiver. Spending time on a fat rockered ski won't hurt your skills that much, so long as that's not ALL you do and you also spend time on the skinny trainers.
so if you get better at powder skiing by skiing skinny skis in powder, wouldnt you get better at hardpack skiing by skiing fat skis on hardpack?
The answer to either is they are both wrong well kiinda off, but at the very least your logical is pretty flawed. I also contend the invention of grooming ruined ski design.