Top down organisation is slow, bureaucratic, and often is bottlenecked for decisions. Inevitably, unless you have monopoly or other form of stickiness, you are quickly outcompeted by the newer nimble organisation. (Hence why companies spend a lot on the stickiness aspect, e.g. Word proprietary format)

Not saying that “flat” works better (or scales). What does work better (with some other downsides) is a distributed system of companies (each internal company operating independently). Still lots of politics around getting the “budget”, still plenty of places to fall down with cross cutting concerns and integrations. Much like a microservice arch vs a monolith, the trade offs can be beneficial at scale.

I’m not sure if Meta is trying to run this way.