Your stock grants are not a bonus/retention plan simply because you believe your cash compensation is at or above market. Pre-IPO stock grants are a lottery ticket. Period.
Here's an exit scenario: your company sells for $50 million after four years[1]. Assuming no dilution and no liquidation preferences, an employee with 0.25% earns $125,000 pre-tax, the equivalent of a $31,250/year bonus that was never guaranteed and deferred for four years.
Why would you think this to be a strong driver of retention for in-demand employees with "realistic worldviews"? In today's market, your best employees can probably get 50-100% of that hypothetical annual bonus in real cash just by switching jobs.
[1] Your company isn't likely to have a liquidity event, but if it does exit, the value of the event is likely to be $50 million or under according to exit data in recent years.