Just a few things to improve duels, really.
Make the first two duellers random
Currently, at least in FFA, whoever joins the game first are the first two duellers. This favours people with fast computers/have already loaded the map.
In tie rounds, don't choose the winner for the next round
Currently when there's a tie in a round, it seems the next two players are chosen. This can include the current winner (the person with the most points) or the person who won the previous round.
This seems pretty unfair, especially in the latter case as it means they just didn't win a round, but still get to go again.
Force change after winning two rounds (in FFA, already happens in teams)
Currently, duel runs a winner-stays on system, which is fine when you have 3 players. When you have more than 3 and a large skill disparity, it means the less players never get any points (or chance to score any really). If you've got a setup where say, A > B, A > C but C > B. And a duel exists where A v C can't get points because they lose to A, and will never get the chance to fight B.
This'll also make game play less boring for lesser players in large duels, who have to wait for every player before them to duel by just moving through the queue quicker.