Maybe I'm just missing the question.
I'm going to use strat-o-matic again for references.
Batters have either N or W (normal/weak) power vs RH and LH pitching. Those N and W are used in super advanced rules regarding ballpark effects. The end result is more realistic power numbers vs respective handedness of the pitchers.
If a player hits 20 HR in a season, 10 vs LH and 10 vs RH, his RH power rating might be W because you face RHP around 70 pct of the time. That batter in MLB The Show should have MUCH higher power vs LH than RH regardless of the handedness of the batter.
MLB has power vs L and R. It also has Contact vs L and R. Vision is universal. I think MLB the show is doing it correctly to reflect the batter's ability more often than not.
MLB the show has to consider SLG in their power, not just HR. That's why a guy like 94 Mattingly is rated properly. He had excellent doubles numbers against LH that year, and the reverse power splits reflect that.