Earlier quoted context omitted.
From experience, that's not true. A bonus of $N is worth $N. A stock grant of $N has turned out to be worth $2.5*N or even more, by the time it finishes vesting. 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 wou…
If you get the cash immediately, then you still buy the stock on the market if you expect it to go up. If the cash also comes on a vesting schedule, if you expect the stock to go up, you could buy call options on the market with expiries that match the original schedule, at the current strike price. Of course this has much more friction and some cost.
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.