Click here to see how unusual his home/road splits were and how it affects is estimated value.
Now let's take a look at Yankee Splits from 1947-51 (I don't think the Baseball Reference Play Index has much data on these breakdowns before 1947).
Yankee RHBs actually did just a bit better on the road (an OPS of .005 better). We see a drop off for their LHBs (OPS falls .019).
But opposition RHBs had an OPS that was .102 higher at their home parks than in Yankee Stadium.. For opposition LHBs it was only .047 better.
So their is evidence that Yankee Stadium hurt RHBs and that a simple park effect may not accurately adjust their stats.