I won't say I ever had a life changing eureka moment yet. Nothing compared to names you mentioned. But I agree with the premise you suggest in this post. Some of the cool creative ideas have come to me when I wasn't really stressing about them. Same is true for my wife, who is an artist by profession. I have noticed how all her creative insights make her draw really cool stuff when she is not worked up about doing them. (@mycrimsonhues if you ever read this, trust me I now understand why you procrastinate so much before making awesome paintings, and why you say you need it to come up with ideas).
Anyhow, I have also noticed this lack of super awesome social skills in many creative minds. I guess it may fit the hypothesis of artistic minds' frontal cortex not inhibiting their eureka moments. Though many times I have also noticed that lack of social skills stands in the way of their success. I think someone should look into this aspect for sure.
Coming to focused thinking vs impulsive aha moments. I don't think focus thinking only inhibits the aha moments. I noticed something when I used to play cricket in my teenage. I was bowler and everytime I impulsively decided where I want the ball to bounce it would bounce exactly there, but if I focused on reproducing it calculated in my head on how to do it, it won't. Then few years later I read this book - Phantoms in the brain by VS Ramachandran. There he suggested this experiment you can do anytime. You think of throwing a ball or a piece of paper in some basket. You throw it and it falls right there. However when you think too much on aiming it, it might not. So what's up with this focused thinking ruining aims and maybe even Aha moments?
I am not a big fan of the left brain, right brain hypothesis. I will talk about it some other time. However, I would also like you to look at this study - this study was done by Beaty et al., 2018. In this paper they show analysed the whole brain connectome of people with different creative abilities. They show that those with highly creative brain have long range networks between distant brain regions, some of which you mentioned in this post.
Thanks once again for sharing these awesome insights on the subject of creativity. Loved this post. I must say it was quite creatively put out.