True, but ... There are more acronyms in the enduser market using C, F, T or the other so-called premium letters than there are using so-called bad letters like Z, Y, Q, X. Although the enduser prices for DAC.xxx might be the same as for QZY.xxx chances of selling DAC.xxx to an enduser are much higher because there are more endusers using this acronym.
Not the enduser price determines what makes a letter premium, but the chances of selling a name with this letter to an enduser within a certain amount of time. If the market for this name/acronym is big it is easier to sell. If the market is very very small, the name/acronym is much harder to sell. This chance of selling is what determines the premiumness of a letter. This premiumness should therefore be reflected in resellerprices, but not in enduserprices.
So my conclusion is that some letters are premium and others are not, but this only affects resellerprices. It does not affect enduserprices, but it does have a relation with the chances of selling to an enduser. Imo the premiums for the western world are : ABCDEFGHILMNOPRSTU.