I think much of what people are trying to say here is that there is no such thin...

I think much of what people are trying to say here is that there is no such thing as a labor shortage in any industry (assuming no artificial wage controls). Also, in the USA you often hear about insufficient supply of workers in certain work categories: software engineer, nurse, teacher. Are those the very highest paid work categories? If not, why aren't the highest paid categories said to be suffering from insufficient supply?

You are of course right that the ratio of profit per employee and salary is irrelevant.