Funny you mention Oban, we do use it at work as well, and first thing Oban tells you is to either use Redis as a notifier or resort to polling for jobs and just not notify.

https://hexdocs.pm/oban/scaling.html

I don't think that Oban is telling you to always use Redis. I think what they're saying is if you reach a certain scale where you're feeling the pain of the default notifier you could use Oban.Notifiers.PG as long as your application is running as a cluster. If you don't run it as a cluster, then you might have to reach for Redis. But then it's more about not running a cluster.