What about this?
Match between Player A vs Player B
A match consist of 3 round.
A hero can only be used once in a match so they have to use different attack heroes for each round.
In a round, the 2 players attack each other’s defense once. Each attack victory give 1 point.
If after 2 round a player is leading by 2 points, that player win and we don’t need the 3rd round.
If after 3 round the score is a tie, add another round. Repeat it again until at the end of the round the score is not a tie.