How you present yourself has a very real effect on how you perform. When you stay in pajamas and a t shirt all day you are holding yourself back.
Every now and then, articles pop up that talk about how people who work at home perform better when they actually wear work clothes. My suspicion is that this is simply the PR industry at work, hired by companies that sell work attire.
There are many studies that show habits are an integral part of being human. I like the 'elephant and rider' metaphor. You have a finite amount of rider time each day to control your elephant. Every time you make a decision or exercise a bit of self control, you use up some rider. Habits drive the elephant too, but don't cost any rider time. If you are working with your habits, you get the elephant to do what you want for free. If you are working against your habits, it costs even more rider time just to do the basics.
So if you are someone that has a habit of wearing sweatpants and a tshirt all day, forcing yourself into business casual clothes costs rider and reduces your potential productivity for that day.
On the other hand, if your habit is to wear work clothes, then getting up in the morning and dressing as if you are going to an office isn't costing you anything. In fact it's probably putting you in the state of mind that you are 'now at work'.
For me personally, 'getting dressed for work' generally means jeans, comfortable shoes, and a button down shirt. Some days a tshirt. If I'm working from home - even on a Saturday for my own sideprojects (as I did today), I get 'dressed for work'. I wake up, take a shower, shave, have breakfast, make the same coffee as a work day, wear the same clothes as a work day, and then go get shit done. Arguably I would expend less physical energy rolling out of bed and sitting in front of my computer, but I would never ever be in the right state of mind.
What you're describing is just sticking a "I'm working" label onto yourself, which could be done with a button-down shirt just as well as with wearing a black t-shirt as long as it is, in your mind, "dressed for work". The part where the PR industry comes in is where people in a customer-facing position - people used to call those "suits" in the 90s for the exact reason of being inappropriately dressed for someone doing production, as opposed to management or sales, work - expect others to conform to their standards instead of the other way around.
In other words, standards of dress tell a lot about whether your organization is engineering-driven or sales/marketing driven, and startup culture - traditionally driven at least in part by technical people - definitely has other standards than banking or consulting.
How comfortable you are has a real effect on how you perform.
How you present yourself is someone else's problem. If it is a problem for someone else then they are affecting how you perform.
I firmly believe meetings are a waste of time.
And a lot of people are bad communicators.