Duels just became irrelevant over time. It's the same thing with endgame. You won't really find any actually good players dueling, unless they're legit bored out of their mind for some weird reason, or want to do some gold bets on duels.
Duels just don't prove what they used to. When your toolkit and numbers all matched up to create a dueling environment where you could actually put on a proper display of skill, that's when people dueled. I believe that the last relevant expansion that had something for low level duels was Cata.
After that, if you wanted actual good twink duels, you'd have to go to the higher level brackets, such as 70s in MoP etc.
With duels, the damage simply needs to be parallel with the amount and quality of buttons available. Otherwise, it's just pointless. It's incredibly evident that current PvP balance is made from an endgame, arena 3v3 perspective (has been for a long time - like it should be). Over time, classes just got narrower and narrower and more specified towards that sort of balance tweaking. We're now at the point where your best opportunity to show off, is within those environments, i.e. group-oriented PvP.