Great blog post, Jo!
For many writers, they take so long to write their books that the market has plenty of time to change (maybe more than once) before they are finished, and trying too hard to fit the market seems pretty useless, since who knows what the market will be by the time they are ready to sell the book?
For someone like you, who writes quickly, I can see how the temptation was so great. And especially once you had an agent telling you what to do.
But now you've gained more confidence in yourself, and, as you say, these days there are more ways than one to reach readers.
You've done a good thing by sharing your experiences with those who might be where you were a few years ago.