Virginia did, indeed, take troops away from the other theaters of war. Take a look at Longstreet’s participation at Chickamauga. Lee sent men by train to the western theater. It was a while before Longstreet joined Lee again—just in time for the Wilderness Campaign.

See Frank M. Mixson’s Reminiscence of a Private ( available on-line for free, or on Amazon for a few bucks)

For a good example of how Virginia sucked the life out of the Confederacy, take a look at the Sherman’s March to the Sea and the Carolina’s campaign.

In my opinion, if Longstreet’s Corps had been available for deployment in South Carolina, the Union’s invasion of South Carolina in January and February would have been stopped at the Salkehatchie River.

Look at the Battle of Rivers’ Bridge, where General O.O. Howard faced a Confederate position that he called, “ The best for defense I ever saw.”

You’re on the right track with your thinking.