Why is it that you claim limits are unworkable? If you can track or enforce it (others have been for years) then couldn't you make it an optional field or checkbox?

Every limit is a commanded outage. We can refund an unexpectedly high bill. We can't refund downtime.

So write "WARNING: your service will go down if you exceed this limit. We cannot provide refunds for this. To avoid outages in the event of unanticipated traffic, do not enter a spend limit."

A learning from the past 6 years: warnings do absolutely nothing. If your answer to a problem is a warning label, you have no answer for the problem.

You’re optimizing for one class of customer by denying another class a choice they explicitly want.

That's true, in the sense that it is true of every coherent business. What would not be a true statement is that we somehow profit from the discomfort of the "disfavored" cohort of customers here. If we could serve them reasonably without making terrible compromises for everybody else, we would do so, and we would profit from that.

Which implies that you cannot reasonably serve the "disfavored" cohort (self-funded startup or small business). In other words, you have admitted that I was correct in that the business model is deliberately aimed at businesses that likely can absorb surprise expenses, and it's not appropriate for others.

I guess business is all about making the right compromises