Great application of first principles. I think it's totally reasonable also, at even most production loads. (Example: My last workplace had a service that constantly roared at 30k events per second, and our DLQs would at most have orders of hundreds of messages in them). We would get paged if a message's age was older than an hour in the queue.

The idea is that if your DLQ has consistently high volume, there is something wrong with your upstream data, or data handling logic, not the architecture.