"You think getting promoted at FAANG gives you an over 50% increase in total comp as the norm?"

It's like $30-50K base each level (~18-25%), but the stock grants can make a huge difference. As a junior engineer you might make ~$35K/year in stock grants; at staff it's like $200K+; and at principal it's $600K+. In total comp you can easily go from ~$350K/year at senior to $500K at staff to $750K at senior staff to $1M at principal, which is close to 50% each time.

Note that the biggest benefit is that getting promoted opens you up to having more negotiating leverage. If the company doesn't want to keep you or if they're sure they'll keep you anyway, then sure, you'll be getting < 10% raises. Same if you came in at a very high baseline because of savvy negotiating or lots of competing offers. But if you're managing a critical team with a sustained record of high performance and then you get an offer elsewhere, that's what opens you up to those $M+ stock counteroffers. Junior engineers are not going to get that regardless of performance, because they just aren't that important to the business.