Having the wrong width bars for many different types might cause one to have very bent or otherwise incorrect hand/wrist position that is not a somewhat neutral position. The 42 cm wide bars on my new bike were making it difficult to keep my wrists straight with my hands and forearms, so I changed to 38 cm wide drops and haven't had an issue with that since.
In the days prior to STI's... which for me was 2016, I'd ride frequently with my hands on the horizontal part of the drop bar and frequently would find my hands rotated down with the wrists very bent and getting sore. That's perhaps why I see no benefit for a flat bar on a bike intended to be ridden for several hours at a time.