Cap tables are indeed very complex. Often there's also a preference on preferred stock, meaning that the preferred gets a minimum return (often 300% or 400%) before the common gets anything.

Fully agreed with the other comments: ignore equity in early stage startups and go for a market rate salary.

The one situation where I would take a lower salary is if there's concrete plans that a company will go public within 12 months, and you're going to be in a senior enough job that you'll be in the know about it.