Well, for fairness, duels should be played with random heroes. This way, you can rely on luck (your own), and you also learn to play with all the heroes, not just one or always choosing a counter-hero. In general, I think many have encountered a situation where you choose a hero, your opponent changes, you change, they change, and so on. In the end, they choose randomly. And in the game itself, the balance is good; I haven't noticed any serious (or even minor) flaws in it, especially compared to version 1.0...
P.S.: As far as I know, the beta test for patch 3.1 is currently underway.