I think that I should modify my earlier post.
Obviously people differ as to their muscles and skeletons.
Equally, something like regular rowing, archery, process work can modify muscles and bones.
Straight bars are fine for BMX etc. where a maximum of control and leverage are needed, maybe only for short periods, but they can put arms, shoulders and wrists into unnatural positions that lead to fatigue on long rides.
I notice that some straight bars have had end grips fitted that are at right angles to the bars.
Presumably to give some relief on longer rides.
As a test, sit down and put your arms out in front of you, parallel to the ground.
Make imaginary gripping shapes of your hands and lower them to about belt height.
Observe how they are when comfortable and relaxed. That is the ideal position for your bars on long journeys.