I think it's there just to give you one more option. Besides, it looks pretty cool B-)
When playing with a duellist-champion, though, the runic blade has a very attractive ability: it increases the power of its enchantment by a ton. Once I got a projecting runic blade, and I could hit enemies all the way across large rooms. Very entertaining!
For a battlemage, hitting with a warding staff will heal all wards. That can make a high-level warding staff quite fun to play with, but it does require a bit of strategy and luck.