I don't know, I just don't buy that writing more means you get better. I'm sure that if someone writes 10x more songs there might be something good to come out of it. But isn't that simply a result of volume as opposed to actual improvement? I look at it sort of like playing golf. I can go to a driving range and hit 100 balls. Some of those shots might be very good. Does that mean I suddenly got better, or was it just because I was bound to hit a few good ones eventually? I won't consistently get better without some kind of correction. But with songwriting, where does the correction come from? That's up to the writer I guess. The OP suggests you post up rough recordings and solicit opinions. I guess that's one way if you really care what others think, as most songwriters do, but is that making you a better writer, or just better at appealing to masses? This is where I take issue with people proclaiming that songwriting has to have rules and regulations and some songs are good and some are bad. It all depends on your end goal. If sales and mass appeal are your end game, then you're gonna have to write something that appeases the masses. That means you will have to consider their opinions over your own. That means you might have sacrifice a little of yourself to reach your goal. For some people that's simply not acceptable and they go their own way, staying true to themselves but never really getting anywhere. And for a very select few, they win both ways. So yeah, maybe the OP has a point. Just write a bunch of shit, churn that shit out, throw it at the wall, and see what sticks. One of those pieces of shit is bound to stick like I'm bound to eventually hit one good golf shot.
For me personally, I'd rather take my time and write songs that I'm 100% happy with. Quality over quantity. Until someone that I feel is better than me tells me otherwise, I'm staying the course.