First of all given the issues with reproducibility within both hard sciences and especially soft sciences I will have to take any results from reading research with a grain of salt until I am able to actually read the specifics of any study. But even for purposes here if I say I accept the results than still the best it can produce regarding a fixed character length is a number which best meets the need of the population as a whole. Which means it might not be the optimal number for me. The great thing about my computer is that I can adjust windows and text view sizes to what I find optimal for myself. It is not unreasonable to expect text adjust to the setting I have chosen as optimal for myself.

Both the expectation that text will reflow and that 66 character line lengths are too short is not unique to me. A quick Google search returns a large number of hits regarding people looking for ways to have either the emails they send or receive be reflowed in their email app.