You need to change the brawling creatures weekly. It isn't even 2 weeks and we have brawling down to a science where you have a specific set of creatures in a specific order and pretty much always win if your opponent doesn't have this line-up. Here in the 2nd week, I am knocking out some of my opponents 4 creatures in just the 1st round. Yea, I win most my battles. It's just a matter of a short time, others see this strategy and copy it. Then brawing becomes a specific team of specific creatures attacking in a specific way and the fastest team wins. There is already no thought involved. I just push a specific action for each creature in a specific order in each brawl and win most the time.
Because of this, the brawl creatures need to be changed weekly and at the most, bi-weekly, to keep it fresh and interesting.