some of you need to calm down a bit. We all know the random factor will make those weapons hard to get.
we have no clue often those emergency missions will happen. we have no clue how hard the bosses will be.
unles you enter with a full pt and everyone is ok with standard (or lootmaster) rules, you'll have to deal with greed only. Everyone will roll on everything.
Even if a weapon is guaranteed as drop, it's still a 1 of 13 chance to get the weapon you need. and then you have to deal with the random sub stat system.

You can farm diadem all day and night but might not get the weapon you want. and ya we know there will be this guy, that has know clue about his job that will rock the 280 weapon...

on top of all of that all that weapon will do is giving you something for leveling in stormblood. it's not needed for anything in the game atm.