That's a valid point. There is definitely some danger that we get to thinking we know more than we do. Hell, I see this regularly with instructors talking about how to counter another style and clearly (to someone who knows the style in question), they are proposing something that would not work. Some of the value in continually exposing ourselves to people in other styles is that they show us on a regular basis how little we know. I've had enough experience with Ueshiba's Aikido, for instance, to know that there's much of their approach I actually don't understand. I've seen people in NGA with little exposure to that art confidently make claims about it that I know to be inaccurate - Dunning-Kruger, indeed. So, exposure to other styles and practitioners is one of the ways to protect against D-K. You see this in BJJ, and it's one of the things you recommend about the art, in general. It's something Drop Bear sees in MMA, and he similarly recommends it. People interact between schools/gyms, so if you're not as good as you think you are, someone will help you improve your awareness pretty soon. This is the same thing we're talking about with interaction between styles.I agree with everything you wrote, but it brought a question to mind. Does "knowing about" or occasional exposure to things (as opposed to committed study) really make one more well rounded? I mean, reading this forum for years has brought us all to at least a moderate degree of intellectual familiarity with a lot of styles, training models and perspectives. But I wouldn't go so far as to say we're more well rounded... well, maybe intellectually more well rounded.
Said a little differently, isn't the danger of dunning-kruger most present when you think you know more than you do. Occasionally exploring another art may give you just enough information to create the unconscious incompetence you're trying to avoid.
And I will argue that what we learn (intellectually) on MT can contribute to us being more well-rounded, in that it makes us aware (if we're willing to be honest with ourselves) of what we do not know. If I just look at videos of Wing Chun, for instance, there's much that seems to make sense. But when I hear someone on the WC forum talk about their power generation, it doesn't make sense to me. Clearly, I know less about the mechanics of WC than my viewing of a video would lead me to believe. Awareness of that lack of understanding is part of being more "well rounded", IMO.