1) Valuation != Liquidity. Even if your company is worth millions and your share is also worth millions, until you have exited you are not going to see much or any of that. Even when you do exit, vesting schedules and taxes make that number much different.
2) Earnings != Salary. If you make a certain amount at exit, that doesn't mean you were being paid an annuity in prior years. As stated in the article, with angel investment 50k salary and with VC 100k. You're still a founder making a salary less than you would in industry, which this article should point out to benchmark things a bit.
It's a tough question to answer and the author is taking a bold step to try and tackle it. However, better methods can and should be used to paint a more realistic picture of what founders earn in the moment rather than being optimistic and backward looking.