Same boat here. I'm 6'10", 260, and athletic. I'm very acutely aware of the shrinking space available on aircraft, and there's precious little that I can do about it. I typically just get an aisle seat and raise the armrest after takeoff (and then spend the whole flight dodging people going to the bathroom and refreshment carts, but it's better than nothing).

There is a problem with heavily obese people taking up significantly more horizontal space than is actually fair, but it's absolutely compounded by the airlines shrinking the per-passenger space to the size of the average passenger.