" . . . there’s no clear path to any kind of promotions.”
Aside from security and (maybe) kitchen, custodial, and maintenance workers, does the White House have any career staffers? Those who stay on for multiple administrations?
Otherwise, it's maybe a 4 year to (at most) 8 year gig, with nearly all positions filled with political appointees - I wouldn't expect much upward mobility for the majority of the lower level people. And with politics playing a role, even if someone is fired or quits, competence is not necessarily the way to earn a promotion to a higher level position. (Note Biden's new press secretary, whose major qualifications seems to be that she's a Black lesbian immigrant.)