I've regarded RabbitMQ as a secret weapon in plain sight for years. The killer reason people don't use it more is it "doesn't scale" to truly enormous sizes, but for anyone with less than a million users it's great. Too many people end up with their own half rolled pubsub via things like grpc, and they'd be far better off using this, particularly in the early stages of development.
How do you manage schema for exchanges, queues, and routing? The pattern seems to be for each client to set up the schema for the parts they touch before hand, but that doesn't scale well. The schema ends up siloed in each project and nobody knows what the current state should be.
Clients creating server topologies does scale very well with the new Khepri metadata store in RabbitMQ 4.0. Applications having an intimate relationship with their middleware (RabbitMQ) and creating flexible routing topologies is one of main strengths of RabbitMQ!
RabbitMQ also allows operators to import (exchange, queue, and binding) definitions on boot.
Server topologies can nowadays even be declared via YAML files in Kubernetes (https://github.com/rabbitmq/messaging-topology-operator). This way all the desired state is in one single place and the Kubernetes operator reconciles such that this declaratively declared desired schema is created within RabbitMQ.