There's no balance in duels, but it's quite possible to play against the Alliance, just 2 stacks of Luminaries is too much :) It's not a given that they'll be nerfed too much.
Well, if not too much, they'll start balancing again, because it's already an overpowered unit. It's enough to prohibit the defensive playstyle and remove the option with two stacks of the Alliance, and problems will begin.
Today, I was testing Inferno, and a winning strategy can only arise if the Heretic gets extremely lucky, because there's no point in taking a Mage... as a result, every turn we focus on maximizing the "Open Gate" spell, which allows us to summon more units than we have, but this "trick" only works with morale; if it triggers 4 times and luck triggers 5-6 times per turn, then the Alliance will start losing due to healing, even with just 2 stacks of Luminaries, and it will start losing even more because all healing spells will have to be used... of course, if the luck modifier also worked in this scenario, it would be hilarious to watch the Alliance lose, but alas, we have what we have. In another similar battle, a complete loss if luck and morale don't trigger at the start... in short, I figured that the chances of Inferno winning against the Alliance are 1 in 20.