Good post f. Look at a position at a legacy as a career. Look at a position at EK as a means to an end. I would say age 45 is the max for returning. That is still a 20 year career. Not all Americans have the option of getting hired at the legacies right now. Might be a drink drive conviction years ago, no college degree (why a reqmnt, who knows), or other skeletons. Or some May have ego issues after being a captain on a 777 or 330/340 and couldn't sit in the right seat of a narrow body.
I will say this, if nonAmerican pilots had the option to return to their home countries and fly for the likes of the US legacies, with the future that appears to await them, I doubt many would remain in DXB. Tax issues and security would be just about the only reasons. Just my opinion.