How does lateral movement work in these companies? If you were an individual researcher (with promotions corresponding to 10 years of experience, let us say) in a prior organization?
Depends on how her/his skills apply to such company / role.
I.e. at FB, you could be E7 by just technical work, but you had to be really good and be able to pick important problems and solve them (say that you are able to design and implement core systems for example). But it's easier to get above E5 by going TL way.
