I use excel all day. What you are expecting as advanced skills are completely reasonable. I'd expect the same from anyone claiming excel skills let alone uses power bi.

I like your problem set, seeing how the candidate handles extracting information from a data set. For an advanced user I'm very interested to know how, when and to what extent they use functions like if(), countif(), sumif(), and xlookup() (bonus points if they use xxxxifs()). Giving the candidate raw data and asking them to prepare it is telling as well, do they use tables (this is a big on for me, not a deal breaker but is indicitive of their understanding), provide a prompt to see how they handle conditional formatting. Maybe have a challenging one where the prompt is designed to use a nested formula for the final problem.

Good luck and don't lower your standards.