Balanced speeds are only necessary for 3 medal clears. If you're experience grinding, then it really doesn't matter. Where you mostly should be concerned are event maps where you repeat for currency gathering. On some of those maps, completely balancing teams by power or attack is detrimental to actually clearing the map. Never mind 3 medal clears, you want efficiency, and you want to make sure you're not going to hit a cockblock on RNG.

In other words, you should really make use of the other 5 alliance slots you're given when creating compositions based on event maps.