After a lot of head scratching, I think I have figured out what Civil War paintings are. They are souvenirs. If we criticize them as art or history, we err.
The contradictions that make them difficult to identify as souvenirs are: (1) they are recently made/manufactured, unlike battlefield artifacts; (2) the historical (factual) content is completely overshadowed by the fantasy arrangement of characters and situations; and (3) they are executed in a contemporary (ahistorical) style.
The painting makes tangible some episode from a familiar story. It affirms the interpretation of that event. It has very low historical content (correct uniforms, the right bridles) and very high historiographical content (interpreting the history of the event).
I remark on this to raise the question of whether Mike Lynaugh is trying to outmaneuver the entire Civil War prints and paintings business with a totally new kind of souvenir. Mixed historical contexts. Another conundrum.