This has bugged me since ACW1. Why do only winning leaders gain experience? To me one of the major aspects of the war was that both sides (especially the Union) were able to winnow out the fops by trial and error. Losing to Lee in 1862 sucked, but the silver lining was the North was able to recognize and promote officers of merit, even if they fought in a losing battle.
In my PBEM as the rebs, it's late 1863 and I still have Humes, Smith and Forney leading corps. I have not been fortunate in my battles, and have yet to promote anybody.
I can understand if this is WAD for playability's sake, but historically losing generals gained battlefield experience too.