I'm an engineer. I'm not saying only sales people should be rewarded. I agree that is asinine.

This is what I'm saying: If a founder builds a business over many months and then hires an employee who can take over 20% of the founder's current workload, that does not mean the employee deserves 20% of the company, IMO. It does not mean that employee is "delivering 20% of the revenue." It merely means the employee is doing 20% of the founder's current work.

Equating percent of current work to percent of equity completely disregards the risks and effort involved in building a sustainable business. Developers tend to overvalue the software assets and undervalue the business relationships and other revenue-producing activities.

Hence my question about how the OP is arriving at their figure.

The whole point of equity is to measure what's invested. You could be doing 20% of the current work of a company, but that does not account for all the past contributions that got the company there in the first place.

Equity is granted on a vesting schedule to approximate the future contributions of a person. If that approximation does not accurately represent the reality over time, it should be reviewed and renegotiated alongside performance.