Are you saying the median total comp for a 7-year total experience Facebook engineer is $1m? If so, what’s your source? (Or what are you claiming? The top decile? The top quartile? Etc.)
3-5 if you don't get promoted after a year and a half or something they mark your packet expectation is you go from 3-5 very quick on average and even faster at the tail.
I did 3-7 in 6 years at Google and it was the fastest in the larger org with >500 people. You can do 4.5 at fb easy.
And yes at fb 7 years would rack lots of engineers 1+ m, even assuming modest gains.
If you don't believe it, it's your choice but not all companies treat employees as average. Google optimizes for average, fb rewards high performers...
I am quite skeptical that the median time for a new-grad hire to get to L7 at FB is 7 years or fewer, but I guess this is something that we could answer with some weekend scraping of LinkedIn. ;)