You mean they're rare in terms of quality, but common in terms of distribution? Or something like that. Seems that's the case.
Since it has been so long since I knew this I will jsut make some things up for an uncut Magic card set sheet.
30 of Common X per sheet
10 of Uncommon Y per sheet
2 of Rare Z per sheet
Unique would be less produced than rare so if they existed in Magic (they do in Yugioh, and other CCGs, but I know little about those games) You might see 1 Unique per 3 sheets printed.
So not only "rare" per distribution or greater scarcity than rare per distribution, as well as numbers printed; but also common in the sense of availability.
Anyone can buy and get X fixed minis by buying the package displayed the mini and it isn't part of the distribution as something hard to get.
So maybe common unique is not as good as saying a fixed rare or common rare.
Paint quality saddens me to say that they have been better for only the rares. Might explain the pitfalls of the game. I also hope that being painted better didn't make something a rare, and the mini was molded with the base prior to painting, and the paint masters should not be voted on what would be rare, but something else to decide even before the mini is made what in the set would be rare.
IE: Make the list of minis and decide what abilities will be had and decide which should be rare, and then make the minis for the list of things needed.
Again sculpt quality should not vary, like paint quality, based on figure rarity as it affects the entire quality of the product line. Fixed minis should not even HAVE a rarity based on random distribution models of collectible games anyway.