I like the idea of using Websockets for IoT devices if you just need a simple communication mechanism.

I wouldn't do it at scale. Message brokers are battle-hardened for messages at scale, have multiple communication styles, especially pub/sub. They are built for messages at scale.

My interest in Websockets is the same as yours — fewer components (no MQTT server). Works well for a simple message flow and I'm ok with reenventing pub/sub for a small number of devices.