I guess there's a difference between talking about how many requests a system is capable of handling, and how many they actually get.

At least when i encountered the discussion initially (some thirty years ago) I'd say we usually talked about how many requests the system was capable of handling. Then requests per second was the obvious unit since a request usually took less than a second to process (obviously depending on the system and so on - but mostly), so using that unit often gave a fairly low, comprehensible number.

Was it ten? A hundred (very impressive)? Perhaps even a thousand (very, very impressive!)?

Multiply those numbers by 60, and there's suddenly a lot more mental gymnastics involved. By 3600 and you're well into "all big numbers look the same" land.