Correct! But this is exactly the definition of "fit."

When I was speaking about "worth" before, naturally one must scope their estimation to the market they're trying to sell to. Market worth is only what the market is willing to pay for something.

If you've got a broad, valuable skillset, but a company can only use 10% of it, they can rightfully scope the role and issue an offer or decline to issue an offer.

What isn't okay, though, is taking the scoped offer and then performing in a far wider capacity - that is the very essence of being undervalued and/or underpaid.

Is it?

I've always looked at fit more from company culture, team dynamic, overall team skill level (A players, B players, etc.) vs. something that's directly associated with a certain compensation package.

Refining: it's a mutual combination of factors, but relative compensation is certainly a strong proxy for some of those factors (skill level, in particular).