Edit Note: I wrote this from the Quickstart rules in anticipation of receiving the Core Rule book for Christmas, and now have a digital copy. Hero points are somewhat more scarce than I had believed.
Initiating a Duel, with a Brute Squad or a Deulist now requires 1 Hero Point. Accepting a duel is free, however only Duelists may initiate Duels. This does balance the overpowered Wound dealing capacity of a Duelist. Some players may become bored when the Deulist rapidly becomes the only player(s) who have any meaningful effect in physical combat. Granted, inventive GM work should alleviate this.
If you cast the Dueling as an extreme athletic endeavor which taxes the player, and state that the Dueling bonus applies to the first burst of action, and then must be fueled by the dramatic action of the scene or foresight of the Deulist then you end up with a system where they do have an awesome advantage but it is checked by their human frailty.
What if a Duelist is required to spend 1 Hero point/Danger Point per round of dueling? Or, simply 1 Hero Point to initiate the duel. After spending all of their hero points (or conserving them), the Deulist is too tired to spend the energy & focus required to pull special maneuvers. Their damage and actions continue under the rules and maneuvers other players are limited to. This should prevent Deulists from chewing up Brute Squads.... because hey, who wants to spend a Hero Point on a Brute Squad unless it really absolutely is that important.
Given the damage imbalance explained by Doctor I believe that the Duelists combat advantage is on par with the advantage of sorcery, which costs a Hero Point to activate. As an added bonus this makes the concession of the other players to the time spent focused solely on the Duelists actions less begrudged, as that player is doing "their thing" and has accordingly paid an equal or higher price for it.
Not to mention incentivizing Duelists to be more forward thinking in the engagement of conflict/violent action.
This should apply to NPC Duelists as well if you use it. Otherwise the imbalance will always be in favor of the NPC Duelist, death, death & dismay.