that kind of achievment I am cool with as already mentioned its for people who already beat the game and it makes end game very tough as you get there at a low level without extra items.
the really brutal achievements are ones that require you to grind for 100s of hours.
try star ocean 4 get 100% battle trophies. - many multiples of 15 hours. by far the hardest achievement I have done. easily 1000+ hours. star ocean 4 100% item creation probably 100+ hours easy ff13 all items - tons of trap and ingot farming 100+ hours easy anything thats completely luck based, as the RNG on the xbox360 or at least on my xbox360 is funky. fable3 all weapons, this one I havent got yet, but I have basically had to make several profiles to get the weapons I have got, beat the game about 8-9 times on 8-9 profiles and still 3-4 weapons missing. its designed for multiplayer trade, I loaf these types of achievements designed to sell gold subs.
on the subject of item grinding rpg;s if an item has a 1% drop rate, I feel on the 100th battle the drop should be gaurantueed to maintain the 1%, but it can easily be 1000s of battles.
also a couple of vesperia ones, one required you to fly baul for a ridicolous amount of time, I basically put a elastic band on my controller and left it going all day, and another with bunny costumes not quite so bad but I doubt anyone would get playing the game normally.