It is in ranked matches that you concentrate on building the best deck for the battle situation.
I believe that tournaments are about building the best deck to counter the opponent's strategy. (Only if you are matched with a strong player in the second round)
But you are right, these are all about balance. It is not absolute. Sometimes you can make a decision based on history. In the end, trusting your gut is what makes the most sense. Even if you lose because of that, it's a good learning experience.