Pretty much every company I’ve been in or know of values a vertical trajectory instead of a horizontal one for its employees i.e becoming a manager nearly always means a faster salary progression than becoming an expert in one or multiple fields.
Why is expertise valued less?
And yet not everyone can become a nuclear engineer or rocket scientist, programm architect, lawyer and so on, so your “experience can be taught, leadership has to be learned” falls apart pretty quickly.
Leadership is not in anyway less then any other job that you can become an expert in. It is just focused on social sciences instead of engineering for example and both can be taught. It’s dumb to say that leadership is something special, its just that it is the more accessible of fields that have a high skill ceiling as it is present in pretty much every work environment.
Tldr, I think your end point is dumb, but I do agree that people management is hard and is definitely a skill. The best leaders are experts in their own right and it is just a matter of contextualising leadership as a skill you can become an expert in.