I'd been treating "drop the non-purchasers first" and "winsorize the top of the distribution" as basically the same cleanup step applied to a revenue metric. They aren't. Once I actually looked at what each one was protecting against, they turned out to be answering different questions — and conflating them was quietly breaking the conditional distribution I actually cared about.
The Muddled Starting Point
The scattered version of what I'd been poking at: whether to decompose conversion rate and expected revenue-given-conversion separately, why looking at the distribution mattered at all...