That is true, but rarity is determined by more than just pure quantity in existence. Demand also has a huge role in determining rarity/scarcity and price. To give you an example, even though there are only 24 Rad Feathers in existence (like the one in my lineup) from what I have heard, they only go for 5000 max because it is not really sought after oddly, but still is worth a lot because of the rarity determined by supply. The Sweet Feather is kind of the opposite. Even though it is more common in terms of supply, demand for it makes it rare/scarce and worth around the same as the Rad Feather. Hope that helps explain why it is worth so much!