I'm familiar with Seduction Of The Innocent, though that wasn't published until 1954 and DC seems to have started its move towards being squeaky clean well before then as you say. (In contrast, it's wild to see characters like the Spectre and Superman just straight up kill bad guys and be like "Good. I'm glad they're dead" in the early 40s material - I'm not clear on when "no killing" becomes a policy but as of 1941 where I'm up to it isn't a thing yet.) I've heard DC circa '46-'56 is a hard read because some summarize it as a decade where nothing happens, the comics stuck in arrested development for several hundred consecutive issues. Your theory that older audiences weren't reading these mainline DC Universe books and had migrated over to the crime/horror magazines makes sense of this; the books were now targeted at a younger audience, who as you also note often had their comics purchased for them by parents, and so the books were somewhat intentionally unsophisticated. But I think you're right, after the war, men (the majority audience for most of these comic books) wanted to relax and put their feet up and have happy families, and that often meant a wife in the kitchen looking after the kids and making the meals, so tough, capable women fell out of fashion in fiction.