In general, if someone with experience in a domain is complaining that something is hard, it's safe to assume that the thing is actually at least kind of hard, and that they aren't just a crybaby about indentation and formatting.
I also assert that if NDFrame.loc were less polymorphic (e.g. if you had a separate accessor like NDFrame.mask for boolean subsetting) it would be easier to use, easier to reason about, easier to teach, easier to document, and easier to write type hints for.
The worst situation is when you want to have multiple return types depending on the argument values, like Pandas' inplace=True. Putting aside the problem of dependent types, even supporting only literal True and False requires you to write out every single overload twice, creating a literal combinatorial explosion of overloads.
And that's also ignoring the whole world of parametric polymorphism required for higher-order functions, factory functions etc.
Maybe the situation is no better in something like C++, but I don't know enough C++ to have an opinion on it.