Im agree that it is very very restrictive and it should be open, but your points are invalid sadly. Actually are just few ones that are untradeable, wich are obtained by dungeon, but why you should need/greed it if cant wear/desynt?. The things obtained by retainer ok you cant choose but seals allways welcomed to buy things u can desynth too. Also the desynthesis give you certain specific materials from an specific item. So there is no need to desynth all in your path.
Also there was stated that desynthesis restriction was most to keep some kind of balance between players as the like now is the specialization for crafting.