I've seen (and see) plenty of expert off-piste skiers (can ski just about anything, and make it look real good) who can't carve a turn to save their life on beautiful corduroy.
There are plenty of people who never move past being intermediate piste-skiers, switch entirely to off-piste (crud, powder, all of it), get really good at off-piste skiing-- but look like a hot mess on a groomer. And not because of the equipment. They've never developed groomer technique-- which while related is different from skiing off-piste. You don't have to be able to link deep, carved turns on piste in order to be able to do beautiful things in the varied conditions of off-piste skiing.
And plenty of people say things like, "after spending so many seasons off-piste, and now skiing groomers with this bad snow year-- I'm realizing how badly my technique has suffered, or how sloppy I've gotten." Just like you see, "after spending XYZ days on the groomers (because of no snow during the first part of the year), I realize how much better my off-piste skiing is now, and how sloppy I'd let my technique get."
(The funny part is that I'm not trying to defend groomer skiing-- I find it boring. It's not my thing. But I see old dudes everyday here in the Alps who, if put on the piste next to plenty a good, young-off-piste skier would slay the young guy technique-wise. And I dare say it'd be easier to teach those old dudes to kill the pow and crud than it would be to teach that young guy to kill the groomer with killer technique.)