I have another friend who has been at 3 startups during this time and deeply regrets leaving his FANG job because he also missed out on millions.
I think the way things are structured, you have to negotiate hard with startups otherwise it's better to stay in FANG. It didn't used to pay this well to be at a big company but the industry has changed. Not sure if things will work its way back, but having a TC of 400k+ as a senior engineer at a tech company is easily achievable these days, so the startups need to give bigger comp packages.