In my experience, the length of the commute flight (up to about 3-4 hours) is less significant than available options, company metal, wx, commuter competition, etc. But anyone could get sick of commuting over decades.

If I were young and lived in SEA, UA vs. AS would be a tough choice (knowing what I know now lol, maybe if I didn't have experience commuting I wouldn't care).

Also the big retirement wave is tapering off and the industry will be back to normal by 2035. Retirement induced seniority progression at the Big 3 is a factor now, but won't be forever.