This seems like it exposes a bias toward thinking in terms of large businesses. (That may be a reasonable bias, at least in the U.S. where it seems like big organizations are only getting bigger and small ones are going out of business.)
In a small business there is less likelihood that the administrative work is meticulously spec'd out. So if an administrative assistant in a small business touching every department, and they are good, chances are work has been offloaded onto them in a way that moves them further from "assisting" and closer to "inexpendable employee who is constantly fleshing out an underspecified business model and iteratively improving it."
I can think of examples where a small business didn't realize this (and some where they went out of business for that reason). But only a handful few where this didn't happen.
If competent administrative assistants in small businesses had any idea of their true value, they'd demand their salary be doubled.
Same logic wrt sales reps. Although in that case, companies at least seem to have realized it and responded by the weirdo pattern of a) providing incentives to attract the best reps, and then b) firing the best reps after a few years on the grounds it's too expensive to keep paying them for consistently hitting their goals and collecting the incentives!