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?
This part is definitely true but I think it misses the point. A single expert can be a force multiplier, or they can be overbearing dead weight. There is the possibility a technical expert wants to micromanage and see every step as it is done (thus holding up work that can be done while the expert is elsewhere).
I conjecture that those skills and attributes that separate the two experts we’ve described is what “good leadership” consists of.
I would never trust a leader who has no technical skills, but neither would I trust a leader who has only technical skills.
You can also have shit leaders that micromanage. What even is your point?
Being a technical expert != being a good leader
There are a set of skills and attributes that enable one to leader well. An ideal leader will have both technical skills and leadership capability, but it is possible for each to exist independently in a person.