I don't know, I'd give the prequels a tad more credit than that, if only because their (very) general plot already existed in the 1970s. (It's not that those ideas are automatically good because they're older; rather, they were developed in concert with the other films, and have also had more time to age in Lucas's mind.) Where there were changes made to this, I think they mostly ended up being less effective. And of course, a ton of stuff was added, some good, some not.

And there are some things that aren't really followed up on thematically. Anakin's motivation - political, personal, what? It varies. This is where there was clearly some basic idea, but more development of a throughline in all three films would have been VERY beneficial.

But I don't think the PT is all in the viewer's head (though I have seen quite a few people go way overboard with their analysis of symbolism).