Of course they all do - and the part you omitted (postseason batting average) probably NEVER comes up. But for some reason, we as fans think postseason stats have lead to any bad contract that went to a player who did have a good postseason. I think in the case of Sandoval, for example, age was a much, much bigger factor. Also his defensive metrics, which were good at the time, played a bigger part than his 3 home run game against Verlander. And probably other factors.
I find it hard to believe anyone would be willing to risk $90mill betting on the future of a player based on one or two weeks. People who make those kinds of risks don’t hold on to their money long enough to buy MLB teams in the first place…