The value of employee equity is approximately zero, but sometimes people get lucky. Don't let these arguments fool you into thinking you're definitely in that 5%, because in the absence of information about the market, the product, and the other people you're working with you're probably in that 95% that makes nothing. By all means update your priors but arguments about expected value assume that all things are equal…
It is worth about what it's worth, and that's not zero, but the difference between the median realized value and the mean realized value (upon which the price is set) is much higher than for public equities.
The above means it can be an irrational bet to take the startup equity if the price you pay in opportunity cost is high relative to your bank. This problem gets worse the longer you stay after that first vesting, but is mitigated by the extrinsic option value of your options (which goes away when you leave and exercise)