Hmm. I agree that Rosa's main flaw is his inflexibility and insistance that "it HAS to be like THIS," but I don't think he's all that bombastic about the Scrooge insights. A Letter From Home is the big one in this instance... I can't remember any other Rosa story that got so blatant about it. And I always felt that by that time, he'd earned that one-and-a-half page where Scrooge stopped denying it all.
The thing that started to annoy me a little with Rosa's later staries was that he was suddenly incapable of writing any story without throwing in a ton or references to his other stories, getting more and more insistant about forcing everything into one continuity -- which really didn't benefit the one-shots much. In the later "treasure hunt" stories, he also sometimes got waaaaay too hung-up about historical accuracy -- to the point where it got in the way of the story.
Still, when reading Don Rosa at the top of his game, I'm more than willing to forgive him these slights.