Duelling is merely a way to articulate, practice and reinforce ACM technique. Naturally, that is usefull in the MA, especially if you are not already familiar with it, are out of practice, or are deficient in particular area and need some objective reinforcement. However, the MA environment requires a wide and varied set of skills beyond that used in duelling to be successful, especially on the mental side of air combat. No amount of duelling will hone your SA and ability to instantly process multiple threats, your decision making process itself in complex engagements or cooperative tactics. All of these skill-sets are required to be successful, only the MA requires all of them to a highly developed degree for true un-mitigated success...
Even my squad, known for their skill, has several people who are fabulous duelists, but who are quite poor performers in the MA. While being good at duelling is certainly an advantage in any forum of air combat, it's not the most important factor for success in the MA. Great flying ability alone is largely defensive in nature, only when combined with great gunnery and good tactics does it become a true offensive weapon. I know a lot of people who are great flyers, but bad shots and/or poor tacticians, they make for slippery targets, but very rarely are they a real threat to dominate an engagement.
The point being, there's a wide and varied skillset required to be successful in the MA, to focus on one in isolation is to take it out of its natural context and pervert it, which is kind of what duelling does in a way. Set duels are to air combat what drawing a circle is to a work of art. The circle may be a subset component of the work of art, but it is not the work of art itself. To examine one small component of a thing in isolation then attempt to extrapolate it to then encompass the whole is to kill a creature and dissect it in order to examine how it lived its life instead of just observing it live. In my opinion, the MA experience is really the closest analog we have to what true air combat was in its totality of required skills and expertise, duelling represents only an analog of a small subset or facet of that totality.