What we are looking at is not balance in general but balance with minimum overall weight and also keeping a good front to rear weight bias. A car that has a lower overall weight,good for and aft,and side to side balance will be at a huge advantage over a heavier car. Todays minimum weights are set due to standards based on nickle metal cells. When lipo takes over, minimum weights will drop so we dont need to add a ton of weights to the cars. Designs will conform and cars will change. Saddle packs are the way to go.
The only reason lipo packs are formed as stick packs right now is to help make the transition from nickle metal to lipo. When cars start to be designed around lipo, stick packs will be forgotten.