I mean, it's at best an average-level senior engineer salary, not some exorbitant L6 Googler salary.

Median salary for a software engineer in the US is ~$133k:

https://www.bls.gov/ooh/computer-and-information-technology/...

I question their data if their p90 value is $211k

I recognize that not everyone makes big tech money, but that's somewhere between entry and mid level at anywhere that can conceivably be called big tech

Define “senior engineer” though..