[rmk]

It's a bit scummy but I doubt you can do a whole lot about it. Companies like Stripe are doing a variant of this where the number of shares that vest will be dynamically adjusted every year based on a target value dollar number. The question is, will they grant you more shares than offered if the stock value goes below that you joined at? Can you get an answer to that in writing? If so, it may be worthwhile to stay, because you essentially make a guaranteed amount of money in the form of equity every year.

EDIT: This is very unusual for large public companies. This is the first time I have heard of such a practice.