> Build a monolith which does everything. Deploy multiple instances. Route booking requests to a subset of the instances. Route other requests to the other instances.

Don't you now have "microservices" bundled together in a single binary - and deployed together? If each of your component exposes different APIs and each instance only handles certain endpoints, then you kind of have microservices - not literally, but it seems the idea is the same.

Simplicity being a benefit, I don't really see how the dynamic traffic routing is a huge benefit vs microservices - you can dynamically scale up/down microservices too.

I am not saying this is a bad approach, by the way, but just that it isn't much different from microservices.