The problem here is the definition of moderate scale and huge amount of usage.
We handle tens of millions of events per year using our primary RDMS as a queue with absolutely no problems at all. The vast majority of projects for most companies aren't going to get bigger than that.
If you have millions of users sending out tens or hundreds of messages per day, sure, that's a huge amount of usage.
The problem here is the definition of moderate scale and huge amount of usage.
We handle tens of millions of events per year using our primary RDMS as a queue with absolutely no problems at all. The vast majority of projects for most companies aren't going to get bigger than that.
If you have millions of users sending out tens or hundreds of messages per day, sure, that's a huge amount of usage.