In the highest comp regions (where new revenue generating projects almost always get staffed) it’s a common ballpark estimate of the allin cost of a SWE including all benefits, office, hiring, infra costs, ancillary roles. Consider that a senior SWE alone is pulling about $400k in direct comp. Also consider Google’s total spending per employee (not even just SWE) is about $1mm and many of those are not engineers or in high comp regions. Of course a new org with no big sales/marketing/compute costs will have different cost structure vs search ads but it really is a workable ballpark.
Anyone can sound confident on the internet, but you don't seem to have anything to back it up. In my experience, 1 million per SWE in the Bay Area is actually about right across the industry.
You can look at public numbers to see that Google's revenue per __global__ employee is about 1.5 M and of that about 400 k is net income. SWEs in California make a lot more than the average global employee.
Costs also include server/DC/sales/marketing etc. you can’t include the server cost of say google maps as part of the people-headcount costs of google maps.