Meh, as a native Dutch speaker auxiliary verbs feel really utilitarian to me, and not particularly fancy - like you said, that’s highly subjective.
As for cases, I didn’t say Latin or German had the most, but just that I think they’re fancy and that Latin has them while French doesn’t.
It’s kinda funny, I’m Flemish and a lot of French loan words (ambriage, merci, nondedju = nom de dieu to name a few) are mainly used in dialect, and therefore don’t make you sounds sophisticated or worldly at all.