Vorlons are probably the easiest race to balance across the priorities - the ships only have one gun, the race only has two guns, they don't have any variation in hull, traits etc.
The Vorlon frigate had to fit between the transport and the destoyer. Too good, and why take the destroyer, too weak and why take it at all.
It was intended to fill a gap in the Vorlon fleet, but since the FAP splits are changing and spliting points down is easier, there may not be much use for it at all.