I've been on clipless since I started riding (17 years ago). Not until about last year I made a switch back to flats. As modern mountain bikes are getting more capable handling multiple terains, I started going airborn a little bit more. I've never had any issues clipping out while on clipless, even on some of the worst situation. And then last year, I had an incident where I need to bail off my bike on a jump and couldn't. I end up crashing but luckily, I only had minor injury.
That made me decide to try on flats. And I'm glad I did. I found out that there are a lot of thing I've been doing 'wrong' while I'm on clipsless. Riding on flats forced me to learn on the proper technique of how to do a bunnyhop, etc. It also gives me more confident especially going through jump trails.
I don't think one type of pedals is better vs. the other. It's all depending on the type of riding you do and the type of trails. I say one definitely complement the other. I believe that if you can master both, you can be a better rider vs. just knowing how to ride one type of pedal. I still ride both depending on the trails, etc.