In all fairness, a LOT of this was copied over from the military. From ranks to "High Year Tenure" (aka "Up or Out") nothing here is particularly innovative.

Amazon had the concept of terminal role (SDE2, but I’ve heard it has changed) long before facebook existed.

In my experience a lot of tech companies, at least in the Bay Area, have all copied this system.

I believe L5 was Google's terminal role at one point (over a decade ago) - not sure if it's changed since then.