Google/Facebooks earnings are so high they can afford to be wildly wasteful with headcount and still be market leaders

Those two are perfect examples of burning insane amounts of money and still showing profits beyond that... Whole metaverse investment. And all the products that Google has abandoned. Even returning all the payments like Stadia...

If you sort by number of employees you get companies where those employees aren't in R&D divisions.

Their comment reads to me as if businesses hire employees (regardless of the work they do, since we are discussing employees that don't do anything) because investors consider employees as R&D (even useless ones).

Either way, there is no data I have seen to suggest market cap correlates with number of employees. The strongest correlation I see is to net income (aka profit), and after that would be growing revenues and/or market share.