You’d have to have some facts about the normal battleground states, and Virginia and NC and others that went from red to blue. Nationwide totals don’t mean anything, and the stay at home conservatives would have been most critical in the closest states, and the red to blue states.
I haven’t seen any data that really provides what’s needed to analyze those factors.
I agree that a much more comprehensive comparison would be insightful. However, I think you would reach the same conclusion. John McCain was a rotten candidate. The loss was completely his fault, not the fault of conservative voters.