The thing you did wrong here was not conceding on turn 2. Seriously. This brawl is easy to farm wins with because you just concede early until you get an insane start and then your opponent concedes early. 5 min games should be the norm.
That makes the most sense. Went 0-5 just letting my opponents absolutely destroy me, then finally had 3 huge legendaries in my opening hand to close out the last game.