How you feel, particularly the intrinsic impacts on self-perception and focus, are definitely backed up by the stories in the article and others I’ve heard.
The experiment is an interesting idea, but would be difficult to do a controlled enough experiment. The closest analogy is actually that NOT dressing at least hasn’t seemed to impede new market entrants from disrupting well-dressed incumbents — even if you can’t say that it’s HELPED. So there may be a correlation/causation fallacy there.
For the instrinsic motives, I haven’t seen any consistency around how dressing formally impacts a lack of self-confidence.
For the extrinsic motives, it’s definitely situation-specific. In finance, real estate, and other industries where the consumer needs to trust you in your competence for success it may have more of an impact than in industries where it’s more about trusting your motives. Anecdotally, if I see someone in a professional setting dressed formally my first reaction is “this person probably wants to make money off of me somehow, which means that their incentives may not be aligned with my goals”. If I see someone dressed less formally, it may or may not impact my perception of their competence but it doesn’t reflect on motives. This is probably due to my sales background, where well-dressed usually meant commission-based.
For me it comes down to how it makes you feel and how it makes your audience feel. If you’re uncomfortable with how you’re dressed, it’s a problem. But if the audience is uncomfortable with how you’re dressed, it’s also a problem. Some people find it less intimidating and more relatable to have a relaxed dress. Some people find that unacceptable and indicative of a lack of personal standards and attention to detail.
If you know your audience and know yourself, you need not fear the outcome of a thousand meetings ;)
The easiest way to test this would be to use the same experimental designs used to measure racial biases, to at least answer those same questions around trust/fear and respect.
If you design a better experiment though, count me in!