That's just the point. Guessing is NOT the best option - exactly b/c you guess wrong or get faked out 2/3 of the time. You're essentially contradicting yourself, because it would then actually BE almost a given if guessing WERE the best option.
Most penalties are saved not b/c of a lucky guess, but b/c of skill or lack thereof by either the shooter or a goalie. Anyway, being a goalie all my life, I'm obviously biased.
As for PK vs , to each his own. But I think PK's are more "pure". Also shootouts would go much longer than PKs. Not everyone is Messi ... or even David Luiz
It'd go on forever until someone hit one.