Maybe.

On the other hand, in economy on some planes I just literally don't fit in a forward direction because of femur length and cycling muscles, I don't fit in a sideways direction either because of broad shoulders and arm muscles, and I don't comfortably fit vertically on some planes with fixed-position headrests which push into the middle of my shoulder blades and have me hunched the whole flight.

I'm also not _that_ big. I'm 6'2" and have lived my life moderately actively. That's it. I'm biased, but I believe economy should be designed so that I can fit too.

If you agree with that premise, that'd leave plenty of space for most 250lb people too, and there'd be no reason to exclude them.