Sean, you could say that that proves that the NL can't pitch, or you could use the same to make a case that the NL can't hit.
I think the drop in ERA's shows the latter, even if you took out the pitcher batting.
Look at some of the guys hitting 7th, 8th in the NL. Furthermore, look at some of the guys hitting 3rd and 4th.
In my opinion, this is where you see the true disparity.