Earlier quoted context omitted.
That number is too high. If you restrict to the FAANG companies, though, it is only a small overestimate. See https://www.levels.fyi/ and select Google. There an L5 represents an "experienced" engineer with at least 4-5 years of experience, and total comp is $350k. Apple, Amazon, Facebook, and Microsoft are similar.
Yeah $400K is high L5. Not uncommon, but slightly above average. It's possible that if you average all engineers you'd get something close to $400K, but L3 and L4 salaries would bring that value down. In surveys L5 makes up the majority of the engineering workforce in these companies, and L3\L4 have a bigger representation than L6+, so it's unlikely that the average TC is $400K.
[0] https://www.levels.fyi/?compare=Uber,Google,Microsoft&track=...