From what I remember of the original release notes for Desynthesis, your desynth level is capped in relation to what level your actual crafting class level is. Unfortunately I can't find any wiki pages that state whether or not this is the case after some searching. Leveling Culinarian isn't all that bad though, all its cross-class skills are very useful if you have any interest in crafting.

(Great name by the way, haha)