I've been a member of a writing group a couple of times very early in my career. My spouse was in one quite recently. I have very mixed feelings about your comment.

In my experience in the arts, specifically music, photography, and writing, good artists are good artists because they know all of the detail and nuance of their work and they continue to be dicks to themselves. A good artist is never happy no matter what they create or what the reaction is, otherwise they would stop improving. Beethoven once famously played a piano recital so poignant that many in the audience were weeping. When finished, he stood up and laughed at them for being so simple-minded and easily manipulated.

Of course, that's just a broad generalization, and there's no excuse for being a dick to others. (Unless they ask for it). I think, however, it draws in stark relief the central question in your comment: are writers' groups for encouragement or improvement? You mentioned a bit of both, but to my untrained ear that sounds like a recipe for mediocrity. Being just motivated enough to produce various works of art that most people in your social group would never criticize to your face? That's not a personal goal.

So I think we're back to the topic of this essay, editors. Editors are there to negotiate what the author wants to do with how the world at large can consume it. They're not there to create or give their own voice. They're there to assume the role of author and advise them what needs to happen for others to better consume the art they make.

I had a friend once who loved taking pictures, as I do. We were mods on a local forum and both of us loved sharing our pictures. (This was in the early blogger days) Eventually news and politics started taking over, so we both left. He went on to do his own thing. I'll never forget what a mutual friend said about him: he just wants people to praise his pictures. Nothing else really matters. He ended up making a bit of a living doing just that. He never became famous but he understood that it was the social praise he was chasing and not the art. I consider a lot of the stuff he did cartoonish but it worked for him. To your point, he became good enough for his social group to be praised and talked about, but no more.

My best editors have always been both inside my head and brutal. They knew where I was going and they weren't shy about redlining the shit out of my text to help me get there. That hurt my feelings a lot and another person might have given up. I found it transformative. ymmv