It's more like Kafka or Pulsar in terms of being the message streaming infrastructure (so an append-only log, not the message broker like, e.g., raw RabbitMQ). I think that the main docs page should give you a good understanding of how the data is stored/organized https://iggy.apache.org/docs/ - for example, on top of the topics, we also have "stream" which is just an extra hierarchy that can be used for something like multi-tenancy isolation or anything else depending on the use case. And yes, there's a built-in RBAC (read/manage particular streams, topics, servers, etc.). As for protocols, we have native support for TCP, QUIC, WebSocket (these 3 are stateful binary protocols), and HTTP as well.
There are a bunch of things that sum up to the overall performance gains - using Rust, thread-per-core architecture + shared-nothing (think of Seastar), custom zero-copy serialization, io_uring for disk * network I/O, and VSR-based consensus (inspired by TigerBeetle) - we simply build all this stuff from the ground up to make the most out of modern hardware and Kernel features, with a custom protocol on top (but the Kafka proxy/gateway is also WiP). And there are also connectors (sink, source), benchmarking runtime, CLI and so on.