Even seasoned experts, will find creativity in jam sessions, stuff that they wouldn't have found by themselves. How hard is this to understand ?
I agree that adversarial interactions can produce results. That's not what the OP is saying. What the OP is saying is that you need a whole lot of self understanding to create good work in the space of writing.
The article essentially suggests that considerable solitude is required to really take one's writing to a higher place. That might be the true, or it might not be true, and it depends on how we define 'good writing'. But we can agree that it's not so easy to dismiss.
On the other hand, the title plainly states: 'creativity requires solitude'. That's a clear-cut statement. And it's extremely debatable. Not to mention that Rilke never even said that.