In fact, that was untrue. Darius' rating of it was actually much higher than it objectively deserved when compared to his own means.
One first should note the difference between Itemancing/Transmutation and the Material element.
Firstly, cost. Transmutation had its own currency in form of Conversion Points, a free but limited resource that was refreshed every day to a certain limit.
Itemancing and the Material Element required an investment in form of mana, a free resource that was not limited, always present, and ever regenerating.
In this regard, Itemancing and the Material element won out over Transmutation.
Secondly, utility. Transmutation could be accessed from anywhere and used on anything, changing it to whatever you wanted as long as you had the CP.
Itemancing could be used anywhere and on any item, to do a limited number of functions related to your progress in the class.