I'm doing a PhD now, after a ~30Y gap since my MSc, in the interim running start-ups, working in defence, oil, banking, Internet and energy saving.

I have been entirely happy being "just" a sysadmin and a developer at times, and never took them as 9-to-5 minimum thinking jobs.

Please don't assume that all jobs that you haven't done are trivial and non-intellectual and beneath you. You wouldn't be alone in doing it, but it isn't helpful.