I doubt that the truly best engineers work there. But certainly at their scale you need really good ones at least.

They also have a huge need for speed. Shipping faster and winning a market is worth 10s of million in annual revenue and billions in valuation.

A lot of this is resume driven development as well. Solving a hard problem, even if it's an invented one, looks good on your resume. So does using the latest and greatest tech stack instead of a boring but functional one.