Instagram, Dropbox, many of the major tech companies still use a monolith.

Or you can think of it as trunk/branch architecture. One main "trunk" service and other branch services augmenting it, which is a simpler thing to reason about.

Now imagine a small shop of 20 devs deciding to build something more complicated.

They actually use a python monolith unless it's changed recently. See e.g. https://instagram-engineering.com/static-analysis-at-scale-a...

Meta deploys as "microservices" with multiple monorepos...

Binaries are deployed and scaled independently as thrift services.

Tons of rpc.