I don't think it's necessarily fair to assign attributes gleaned from those in your bubble to the overarching whole.
For the most part, I agree with you, but the idea is that a given look (Spalla camicia, in this case) is entirely out of place is a tad overblown. I know and interact with a decent amount of Wall Street/hedge fund folks, and they're certainly a mixed bag from my experience. Some are among the lines of your thinking, some wear meh, relatively ill fitting suits, and some are cool with wearing a shirt, sweater, and khakis.
I KNOW (again, this is only my experience, nothing more) a Spalla camicia suit, regardless of the fabric, design, etc would be seen as overdressed in some of those circles. However, to your argument, they would also be seen as out of place in others.
No one is talking about being overdressed. You are missing the point completely.