Thanks for the reply - I did not mean to rant, but, unfortunately, this is in context of a B2B service, and the other side are most commonly IT teams of customers.

There are, of course, both very capable and professional people, and also kind people who are keen to react / learn, but we've also had situations where 429s result in complaints to their management how our API "doesn't work", "is unreliable" and then demanding refunds / threatening legal action etc...

One example was sending 1.3M update requests a day to manage state of ~60 entities, that have a total of 3 possible relevant state transitions - a humble expectation would be several requests/day to update batches of entities.