> 5 orders of magnitude too small for another.

Nitpick on an otherwise good post, but I don’t think there are very many 6billion RPS systems out there, and those that do exist are almost certainly using bespoke, purpose-built tools

The highest I could think of is WhatsApp, which gets ~1.6 million RPS on average, and they use MQTT

Could be base 2. ~1.3M RPS is a lot higher than most will ever require, but still within the realm of possibility.

Maybe there would be more if it were more straightforward to do so?

For reference, I've seen Visa marketing materials that suggest their network can do ~70k TPS. There are not very many systems one could conceive of that could do useful work 1/s for ~every human on the planet.

Fair.