For Erlang I would say that the hard part is not the language itself (maybe a bit because it is influenced by prolog) but because of the mental model. Using concurrency and parallelism as core concepts of the language and understanding that you don't need a lot of the external tools you would with the more mainstream languages is what's hard imo.
Not everything should be beginner friendly. Trying to nerf things because they are not beginner friendly should not be how tools/patterns of languages are designed.
Its ok to have more advanced topic that require more knowledge and that people don't understand from the first moment they see them.