I have a 4k and a 21:9 1440p display and I'm sure anyone who gives 5 seconds to think about it will agree the bottom panel is a total waste of space past the usual 1920px width - unless you have an absurd amount of widgets there.
So not only I agree with the gaps, but I have my panel centered to approx. a third of the display width and there's still plenty of space to fit open windows there.
Full width panel is a legacy choice that just doesn't make much sense with nowadays screens.