It wouldn't be the first time that the L2 store sold something that was either (1.) cheaper to find in game, or (2.) players could get something similar, if not better, for free by doing a quest. The store should have a general disclaimer added to the Enhanced Brooch that a quest for one type of brooch is available in game at no cost. If they did that, though, they'd also have to do it for all of the other items that you get for free via quests and leveling up, like R grade soulshots, blessed spiritshots, etc, etc., etc.
But to play devil's advocate, this game has lots of lazy, willfully ignorant players who want things now without having to work too much for them. Those players tend to play this game with their bank accounts and credit cards, so in a way, NCSoft is just appeasing that segment of their consumer base. No point in leaving them out in the cold and not profiting from their need for convenience.