"when the truly outstanding in other fields are paid a lot less?"
You mean like sports stars?
The command higher fees because having their name attached to a project reduces the amount of marketing expenditure of a project and increases the projects chances of success.
Aside from fees for high-paid actors and directors though there are still a LOT of people needed to produce a quality film: screenwriters, cinematographers etc.
Sports is probably the closest thing we have to a true meritocracy. If you're an incredibly talented baseball player you'll have statistics to back it up.
Because of this I'd wager that almost all the top tier baseball players are currently engaged by major league teams.
However, acting is more subjective. It's much harder to objectively demonstrate that you are a top tier actor, so there are likely many top tier actors available for hire who aren't making millions.
You mean like sports stars?
The command higher fees because having their name attached to a project reduces the amount of marketing expenditure of a project and increases the projects chances of success.
Aside from fees for high-paid actors and directors though there are still a LOT of people needed to produce a quality film: screenwriters, cinematographers etc.