HonestIy I'm not the best at answering this, idk if it's normal for the lower house nobles to be working as lady in waiting.
but from my understanding.
I think you've answered your question with the ranks, since it's the lower powers houses that'd work for the higher power, that'd probably be more useful for them rather than shameful.
Pay would be higher for sure but i think it's also the status and the fact that they have a major power sort of backing them up. They're already a nobel but since they have a stronger one that they're sort of working or affiliated with, that'd make them more stable.
Also just a theory but i think it's probably just a sort of discrimination that was normal in olden times that since royals lived a completely different and luxurious life than 'commoners', it was easier to hire someone that is already used to a nobel lifestyle and that could be controlled easily with their title of nobel in line so they don't misbehave or do something out of order. Minimizing risks of sort.
ladies in waiting are companions, not servants like maids are
so yes it's normal for lower ranked nobles to be ladies in waiting
and being a lady in waiting gets you connections with people with wealth and status, so you get favourable marriages. it's not considered working like the way we understand working i.e., getting a salary and having a 9 to 5
and even then, it's also not shameful to say you worked for someone as a noble. nobility doesn't mean you're automatically rich and privileged, it just means you belong to a class that doesn't pay direct taxes to the king.
also. historical manhwas are notorious for not being at all accurate. (e.g., the dominant religions in europe did not have temples nor state-approved saints like they do in manhwas, no one had a perfect blowout that looked like they came out of a kdrama, dukes didn't lead armies to war etc)
so take everything you read in european type historical manhwas with a boulder of salt. they're more likely based on aesthetic instead of accuracy or function anyway
I've been reading alot of Historical manhwas these past few years and I've always wondered, Why are Ladies-In-Waiting are usually nobles?
Isn't that usually the job for Maids? Is it normal for lower ranking nobles to work for higher ranking nobles? What will they achieve tho? Isn't it shameful to say that you 'worked' for someone as a noble?