Your arguments make sense in the generic case - but since this was a one-off purchase (there aren't more of these "4 creator car set" listings for the same price available), and since the purchase was made by me, who has MISB versions of each car on the shelf, and who has access to FBA, the prices I quoted are accurate as a justification for my purchase of the listing in question. If I list my MISB 10248 F40 on FBA now, I will clear ~$200 minus my purchase price (~$80). Similarly, I will make money on selling the other sets, since I got all of them for significantly below RRP. I'm sure I will end up paying nothing for these 4 cars once the smoke clears, hopefully with some extra money to boot.
That's where I was coming from. And ignoring that, $40 each for these cars in "Used but complete with stickers and instructions" state is IMHO a good price to pay regardless, hence why I posted my purchase in this thread.