I suspect you are not being truthful here. This:

"Each engineer's pay is the product of their skill level, how they negotiated as well as competing offers they had."

Is an assertion. Or at least, it's an assertion if you make the implicit "and nothing else", explicit.

Regardless on where you or I personally come down on the truth value of that statement, it isn't hard to understand why it is controversial.

In this case some would add gender to your list, and it's not immediately obvious or empirically proven that they are wrong (or right).