No, I understand that point of view.
You're missing my point of view that EVERY team usually has at least one or two people who hit for s***...the NL just replaces one of theirs with the pitcher instead of, say, the catcher (current Tek, haha) or a SS or an OF.
There have been pitchers who can hit/bunt at least as well as (current) Tek in terms of getting on base perhaps, tho I know that's probably pretty rare, and it's sure not Penny, haha.
Also, in terms of a pitcher's win/loss record, even if there is a small advantage because a batting pitcher=less runs scored, the other team they're playing will have the same advantage, right, so it could balance out and thus the pitcher's W/L record would not improve substantially.
Lastly, in the NL, since they have to bat, pitchers are more exposed, maybe, to injuries and fatigue.
Still feels to me that in terms of a pitchers W/L record that in the long run it would all kinda balance out.