Could it have gone the other way? Of course, and it's often likely that at startups stock could be worth zero. But at large companies, even with the recent dips in stock prices, employees who joined 2+ years ago are better off with stock grants than they would have been with equivalent fixed-size cash bonuses -- so much so, that would often have to take a pay cut to work anywhere else.
Right and during that vesting period if you had been paid cash you could have invested that money in a wide range of assets that are both more liquid and are not perfectly correlated with your source of income.
Now if we're talking a bonus that would be paid at the end of the vest period such that you can't invest that money until you would have vested anyway then stocks is theoretically going to have increased by the risk free rate, so it's expected value will be higher than the bonus (however it's much higher variance).
Everyone has weird thoughts in their heads about RSUs people the last decade has been insane, and no one remember the last tech crash. The next one will be bigger and when you realize you are getting laid off at the same time that your RSU drop to near zero, it will feel like the variance might not be worth it.
As I wrote elsewhere, who knows? But in the dot-bomb crash, large solvent companies saw their stock tank by 95%. And, by the way, to first approximation no one was hiring so you're not just going to hop to another company.
Hopefully everything will be reasonably fine but I think a lot of people have an unrealistic expectation of worst case scenarios.
With RSU's, you get $400k1.05^4 (4 years of compounded growth)
With cash, assuming you immediately invest the money, you get $100k1.05^4 + $100k1.05^3 + $100k1.05^2 + $100k *1.05
Running those numbers, the RSU's are worth $486,202 at the end and the cash is worth $452563. RSU's appreciated by $86k over the duration, cash appreciated $52k over the duration.
It's the time value of money. Getting it earlier makes it worth more.
Of course most people won't do it because is very risky. Yet getting RSUs has similar risk (or larger as you can lose more than the option premium).
There might be US tax implications that I'm not familiar with of course.
Also I'm not familiar with the US case, but I understand those limitations are contractual not regulatory and thus have no bearing in what's would be optimal for the employee.
If, along those 4 years, your company tanks 25% (Shopify tanked over 50%), you’ll be able to abandon the investment (and get 100k a year of something else), or double down and get more shares (aka dollar cost averaging).