Is the optimal balance rule set in stone?
This will likely create some unbalanced games. Ideally, you want the strongest team members to be on the carry slots, i.e. rock and air so each team has their best chance of winning. Leaving it to random chance isn't good. For example, what if one team has their carry players on the weakest slots, whilst the other team has their carry players on the carry slots. That's an inherent random disadvantage for one team and is generally not good for the tournament as a whole.
Teams should therefore be able to collaborate amongst themselves on who will take up which slots
Many Thanks