What you are suggesting is that when you use a lefty hitter your opponent will stack the lineup with righty hitters that have HUGE platoon splits and kill lefty pitching. Which is OFTEN but NOT ALWAYS true.

I'm not talking about some mediocre lefty here... I'm talking Mike Hampton, who was probably the 2nd best lefty in the game in 1999.

Part of what makes Randy Johnson so dominant is that he kills all lefty hitters. Against righty hitters in 1999 he appears similar to Hampton (at least I think so). Therefore if the aformentioned lineup of right handed lefty killers should beat up on Hampton I would expect them to beat up on Johnson also.

I must be missing something.