Normal Sins of Attrition (level 19 on normal) is of comparable difficulty to this quest on epic. Any of the reaver's refuge quests on elite (level 17 quests on normal) are harder than the quest on epic. This quest is much easier than the only quest I've soloed on epic (last stand), which is to me currently one of, if not the, easiest epics in the game on live.
The quest is way too easy on epic.
The other three difficulties seem about right...not too hard for a prepared party on elite (doesn't require knowledge of the quest, just a competent group) at level, which is right for a f2p quest chain. Normal and hard are understandably easier.