Having clutter in your environment, one thing that the book Goodbye, Things mentioned was that everything in your space 'says' something to you. When you see a book, it might be, "oh why haven't you read me, you bought me with such emphasis months ago." A pair of slippers might say, "put me on so your feet are not cold." A bill laying out, "remember to pay me." By the time you get to your desk or try to do your work, you have so many things competing for your attention, no wonder it is divided.
His experience is that by decluttering, he was more assertive and decisive. He knew what to do and when to do it. Marie Kondo says a similar thing, that the spark joy part of it is life changing. I think there is truth that both of them are dancing around. That a person with clutter may also not have priorities or know how to prioritize. THe external space reflects the internal. The internal reflects the external. Now there may be other things going on, "I know where everything is!" and the room is a mess. Or a person super organized, but unable to do things. But there is disorder in one case, and there is disorder in another case.
Environments have more affect on us than we might think. As high-achieving people, we think that we can overcome anything. Oftentimes we have fought in sub optimal environments to get things done. But having a bad environment, you are constantly swimming against the current. It may make you stronger, but you are not making as much visual progress as someone who is swimming with the current.