I’ve ridden spds since they came out (yes, that old) and recently did a course where the tutor used flats and I was in my clips. I could see where my technique would have been better had I learnt to ride off road on flats so I bought some.
It’s a bot like learning to ski and then someone telling you to try snowboarding because it’s so much more fun… the switch can be painful as you spend the first few (very expensive) weeks on the pistes with a bruised ar$e.
I still have the flats, they are in a box where they belong. My technique was improved by the course but I still use spds.
I don’t think any form of pedal specifically makes you a bad or better rider; it’s how you ride the bike – the pedals don’t do that.