As an author I think this question is on our minds all the time. Should an author change to fit the current market flow? That's always one answer that is difficult to accomplish.
My problem is that I usually write long novels for my time travels and have extensive research for the era and setting of the story. Most of these stories take me over a year to write. Heck, two to three is conceivable from start to finish.
I do try to listen to the market wants and needs, but by the time I do it would mean changing a story. I tried it once and shortened a story. The reaction wasn't what I expected. In fact, it clarified my author self that shortening doesn't work for me. My readers want the full story and if that means a 100k word count then so be it.
I doubt if most authors would agree, but then it is the reader voice that matters to me.