This is horrific for employees. Ben Kuhn already nailed the math here[1]. The optionality embedded in long-dated grants is a huge fraction of total comp at high-growth companies and represent almost the entire right tail of outcomes. It also requires assumptions about the future, which is why companies generally abstain from quantifying what it's worth. It seems like the companies doing this are trying to arb that uncertainty by retaining all of the potential gain for themselves in exchange for a slightly larger nominal income.
Don't do it.