If there's an exotic weapon worth getting, then it's one of the swords. Raze Lighter (solar) is the most useful one imo, followed by Dark Drinker (void). I actually never use the arc sword. The easiest way to get them is to gather all three quests with the warlock, as he has powerful supers for all three elements. Killing the adds and collecting the special resources for a sword (and even more for all three) is a very tiring grind, that is true. If a character has several sword quests, he can however complete the crucible part once for all he has, and also do the final strike once. You just need to be careful to leave all guardians you need for the sword quest alive to the very end of the strike and then quickly kill them all and then Alak'hul.