The two FAANGs I have personal experience with aren't very flexible when it comes to base salary, though. In both cases, during offer negotiations, I was told the base salary is strictly tied to levels of seniority in the organizational hierarchy, so there's effectively no room for maneuvering there.
RSUs were much more flexible, especially after the first couple of years.
RSUs were also a more important part of the compensation. My initial package in one FAANG was about 55% RSUs, 45% cash, and I was told that going forward my RSU component will increase even further, and in particular most bonuses and raises will be granted in RSUs.
So I'm not sure "negotiating hard" is a viable strategy in FAANG compensation discussions. They can be quite generous with RSUs, but cash policy is often strict and inflexible.
To answer your question, simply switch FAANG's when the market is down so you enter at a low price. That's what I've seen so far...