"Remarkably, the classical starting position-despite centuries of cultural selection-lies far from the most balanced configuration."

Right, balance would be one of many parameters that make a game popular. Complexity is even a positive aspect of a game, a simple game with a simple optimal strategy would not be the most popular.

Simplicity of rules is another parameter, the classical configuration is somewhat symmetrical on the Queen King axis, many candidates would provide a rather asymmetrical and hard to remember initial configuration.