Ancalagon
Dusty Dragon
Since it is all based on rarity, it is utterly useless for any campaign that hands out gold instead of magic items, so that the players can choose themselves what they want to buy.
The reason for the fan-effort "Sane Magic Prices" is exactly that the WotC support is entirely random... or as they would say: insane. Winged Boots more rare/expensive than the Broom of Flying? Weapon of Warning uncommon while Vicious Weapon rare?
Are they mad? A Weapon of Warning is a hundred times more valuable than a Vicious Weapon. (171 times more, in Sane's opinion)
While I don't have your... vehemence... I must say that your central premise - that the rarity rating isn't equal to the power - is entirely correct. If memory serve (I'm eating breakfast and I don't feel like getting my books

Now, there may be very valid reason why this is - maybe the vicious weapon is harder to make - or maybe the few magical item creators felt that it sucked and made + 1 weapons instead (haha) and thus it's relatively rare. This difficulty/rarity could drive up the price. In Yoon-Suin's Yellow City, where there are magical item auctions, most of the buyers (and sellers) aren't users of the items, they are collectors! (The slugmen of the Yellow City are very rich, and bored). So for them, the vicious weapon is more valuable that the "I've already have 3 of those" +1 weapon.
BUT, if you want a system where the price of the item is entirely dependent on its *utility* then yes, the rarity = price guidelines of 5e is not going to cut it.
BUT, I would contend that the prices of 3e weren't quite right either
