As someone who flies to FAR limitations daily, I know I would be less fatigued if I was on duty for less than 16 hours but I flew up to, say 10 hours.

For me, it's not the flying that is fatiguing, it's the sitting and waiting. I will be doing a trip with a 5:35 show 1 leg to 3 hour sit then 1 leg to outstation. Because I have to get up so early, it would be easier to keep going rather than hurry up and wait.

The next day, I have another 3 hour sit after an initial early leg, and duty off at 20:40...

More flying and less duty is a better use of my time anyways, I think we have all seen enough airports to last our lifetimes.