Segment uses MySQL as queue not even as DLQ. It works at their scale. So there are many (not all) systems that can tolerate this as queue.

I have simple flow: tasks are order of thousands an hour. I just use postgresql. High visibility, easy requeue, durable store. With appropriate index, it’s perfectly fine. LLM will write skip locked code right first time. Easy local dev. I always reach for Postgres for event bus in low volume system.