You've shifted the goalpost from "any jam session" to "professional jazz musician".
Yes, I'd agree that all professional jazz musicians have spent considerable time working on their craft alone. That doesn't detract from what I was saying. Professional jazz musicians aren't the only type of people who do jam sessions, and they're not the only type of compelling artist.
In fact, even if every single artist in the world had spent considerable time studying alone, that doesn't necessarily mean it's required. The fact is, every single piece of music theory, every single thing you can read from a book or hear from a record, every single practice session, can be done in a group. It may just be that people prefer not to do that, or don't have the resources to do that.
I am very curious now, because you seem to be alluding to it: is there any real world example of any kind of artist who is both "compelling" and did most of their studying or work in a group? Or is this just all in theory, like "Johnny Thousand-Livers"? https://www.smbc-comics.com/comic/organs
The vast majority of human beings throughout time lived in extremely communal situations without separate bedrooms, without sheet music, without books, and without records. Solitude in the home was rarely available. Virtually all folk music around the world was developed in these contexts. We barely know their names or their work, and that's simply because sheet music and historic record were limited to the interests of the rich.
The availability of prolonged solitude to practice an instrument is an aberration in human existence. Modern humans, and the historic rich, do not represent the wider experience of human existence. Unless you think compelling musicians are also an aberration in human existence, I personally believe a wider perspective is needed.
GROHL: Well, I remember we talked about this. I think we were talking about practicing. . . .
STARR: I never practice [laughs].
GROHL: Nor do I! Because I don’t like playing alone. I only like playing when there’s music.
STARR: I’ll play with you all night, but on my own, after two and a quarter seconds, I’m like, “Ugh. That’s not what it’s about.” When I’m doing shows, and people hold up their little seven-year-old: “This is Tommy. He loves you, and he’s taking drum lessons.” And I always say, “I hope he’s not taking too many!”
Yes, I'd agree that all professional jazz musicians have spent considerable time working on their craft alone. That doesn't detract from what I was saying. Professional jazz musicians aren't the only type of people who do jam sessions, and they're not the only type of compelling artist.
In fact, even if every single artist in the world had spent considerable time studying alone, that doesn't necessarily mean it's required. The fact is, every single piece of music theory, every single thing you can read from a book or hear from a record, every single practice session, can be done in a group. It may just be that people prefer not to do that, or don't have the resources to do that.