Dilution of ownership goes in two directions. You pointed out that it could be less valuable than the book value. But if the company does well, then the cost of that dilution actually increases over time.

Closer! Let's say you give me a coupon that I'm able to redeem from you later for 20 dollars.

Do you owe me $20?

This is the closest to what SBC is.

If the options are exercised, you're liable for that expense. It's a delay on the payment of the 20 dollars helping cash flow, and tax code yadda yadda, but you can't pretend that handing out vouchers for money to employees doesn't mean you're not liable for the money from an outsider assessing your financials.

The other way to look at it is that potentially $3.9B worth of stock could be sold on the public market and further dilute the value of the stock.