Not sure I understand why this is a bad habit, its just another way of doing something. Surely the fact you can do that indicates being clipped gives you greater control over bike positioning, a good thing I would have thought.
It just comes down to whether you’re working with the bike, or not. If you ride through a rough section and you’re just being held onto the bike by the SPDs (ie, you’d bounce off without them) then the side effect is that you’re putting extra loads into the bike- pulling it around with you, and making it work harder. If you let yourself get kicked, you effectively kick the bike.
Whereas if you’re not relying on your pedals to attach you- ie you’re on flats, or you’re on SPDs and riding dare I say it a bit better- then you’ll flow along with the bike rather than against it, and give everything an easier time, staying more in control. If you let yourself get kicked, well, good chance you crash- so you learn not to get kicked.
This isn’t a “flats skill” or anything like that, but it’s a skill you pretty much have to learn if you ride flats, whereas with SPDs you can get away with it a bit more. Just like good smooth spinning isn’t an SPD skill but people are probably more likely to end up as pedal mashers if they only ever ride flats.
Course, if it works for you then that’s fine but there might be better ways to do it.
Anyway- in conclusion- ride what you like, riding bikes is good. But if you’re into analysing your riding or looking for ways to improve, then trying the other pedal type can be interesting. And for the OP, if you feel SPDs are holding you back then yes maybe try flats, or maybe work through it on SPDs, they’re both good.