It looks like a bug if not i am sorry i have never noticed this before. Anyways my Enchanter is currently Rank 5 - It lets me enchant a lv29 legendary bow, however it says i need to be rank 12 to enchant a lv19 yellow helmet, and rank 10 to enchant a lv32 legendary armor.
That makes no sense, the lv19 yellow item needs to be rank 12. Again if there are other mechanics in place that i am not seen ignore this message and I am sorry.