I fail to comprehend how this relates to anything you mentioned. You said that if both sides have 12-3 halves, then they are even on both sides. Sure this is pure statistics, but you also fail to realize that there are multiple variables involved with how a round is won or lost. You can not generalize this into pure probability, where say Liquid will win T rounds 80% of the time against Astralis in this match, so they will win 12/15 rounds, while Astralis also wins T rounds 80% of the time, so they will also win 12/15 rounds. This isn't so simple that you can simplify their performances into how many rounds they won, so that rounds won equates to how good they are.
Basically, you are assuming that two teams of AIs are playing against each other with set probabilities of winning a round.