Making it the entire basis for application abstraction is lunacy, the sort of extremely clever idiocy that can only occur in the tech world.
I can only assume it's because he saw his clients doing it and for a consultant the client is always right. (And I think the client was doing it to indulge their hard to get developers who wanted complexity and the freedom to use their programming language of the week)
It feels like a cowboy industry when this is the 'leadership' we have.
Look at the REST/JSON API debacle that has unfolded over the last two decades. It is trivially obvious that REST is both difficult to implement and largely pointless outside of a hypermedia system, but the thought leaders never said a thing about it.
I don’t have a strong opinion on alternatives. GraphQL seems ok for server to server stuff.
Also, in things like kube, it's possible to schedule jobs next to each other so your TCP connection is essentially going over localhost.
There are many tricks you can do to have this even out perform a single process application.