> The more messages you need to process overall, the more attractive a solution centered around monotonically increasing sequences becomes, as it allows for space-efficient duplicate detection and exclusion, no matter how many messages you have.

It should be the opposite: with more messages you want to scale with independent consumers, and a monotonic counter is a disaster for that.

You also don’t need to worry about dropping old messages if you implement your processing to respect the commutative property.