This is an interesting discussion.
I sort of get both opinions.
I think it's probably between collectors, but the revenue is more of an item being sent, like merchandise or a gift.
Can it be a "use" without having provided any function?
It probably shouldn't have been cancelled, but the postal clerk just saw it as an uncancelled stamp and did his job.
Oddly, I had a similar discussion with a local guy who exhibits and is a Judge (Unless I have the judge bit wrong)
I asked him how to handle a group of items that were to me philatelic, but were probably the only uses available
Neopost CVP stamps used to mail neopost unused sheets to me as an
ebay buyer,
Or
From one original purchaser to another.
To me they're philatelic, but nearly every existing cover is.
His opinion was that the stamps were used to mail something being sold, making it a valid commercial use even if it was between two collectors.
I'm still on the fence, and still haven't put together anything on early computer vended postage. - Or postage where the machine printed the postage, so I could include mailomats and similar things.