OMG, I did freelancing for years, and it’s everything you said and more — or should I say less?! BUT I did learn a lot of skills that way, and it saved my ass when I was sick for a long time and that was all I could pull off. I had one six-year-long gig where I learned about an industry (not one i wanted to be in, but…!). But better than that I learned AP style, had a great editor who taught me a lot about writing headlines, using humor, and writing nice, crisp sentences and short paragraphs. And to tell a story to hold the reader just long enough. BUT on the side I started writing novels (2 of those) and then my own blog to keep my friends up to date.
Freelancing can be a good place to start. I asked someone to be my mentor. That helped. I suggest that for other freelancers-want-to-be-real-writers.