I don't see fun and correct as mutually exclusive ... especially where things like banners are concerned. that is a compromise we might run into if the game mechanics throw a barrier at us, but this is something we have complete control over.

No reason why we can't have a banner. Locate something suitable in the refernce material, pick a good background colour, and paint a banner.

40K banners are not ideal if we have something that DOES come frpom the correct sourcebooks.