To follow on from your idea...I'd like to see a 1v1 option as well. You queue up, get matched with someone of similar calibre and it's best of three rounds. Throw in some annoying environmental hazards as well just to keep things interesting - imagine Maelstrom arena with no mobs, just you and one other player.
Each round has a time limit of five minutes - if neither party is dead the person who dealt the most damage wins the round by default, this to discourage the aforementioned 60k Harbinger approach to duelling.
If this becomes a thing, a dmg mitigation cap, health cap, no cp, and a maximum timer must be added, or else it will come to a point where ppl just specc into 60k harbinger builds resulting in forever lasting fights