I disagree. Market research and bouncing ideas off of people is necessary to not get lost in your own sauce.
Stephen King has his wife to bounce ideas off of. But what about single people, or people surrounded by others who hate reading? I think the forum is a solid way to get third party feedback that could be missing.
Be they potential stories, or work in progress, having feedback is good to have. And some stories just lack reader engagement to get any.
See 1-
1. Forums, even reader sections of the forums, are not representative of actual available readers. Regardless of the answer you get, there is a high chance that the result is meaningless.
The feedback you'll get on ideas alone on the forums aren't representative of what the majority of readers may think. This is due to sampling bias. You aren't actually getting a sample of readers, you're getting a sample of readers/authors who use the forum, which is a particular type of person. In fact, I'd be willing to argue that most people who use the forums have strong preferences against what is considered "middling" writing or concepts, despite the fact they do reasonably well.
I don't disagree that bouncing their idea off of someone is a good idea, but I disagree that the forums of SH will actually give the feedback they're looking for when their question is "Would you be interested in reading this?" Forum users often have very strong opinions in certain genres, and if you get one page of responses or less, you're going to end up having a highly unrepresentative sample. It's not actually giving you the feedback you want.
The real bottom line is that you actually do need that friend willing to listen, strangers on the internet cannot fill that purpose. Why? Because every author and even reader is surrounded by more story ideas than they have time to evaluate. Most writers have more story ideas than they have written stories by a large margin, and most readers are spoiled for choice. The value of the idea alone is pretty much nothing, the supply is near limitless. A friend is willing to hear you out despite it being a valueless endeavor for themself, but it constitutes part of the contract of friendship, being a sounding board. So no, I don't think the forums can substitute as a sounding board, and at the very least, they don't substitute as a good alternative, it's a bad one at best.
If you're asking for concrete feedback on aspects from other authors, then it can gain some value, whether it's pacing, tone, grammar, or even the story execution. Even then though, there will be biases assessed as part of internet sample biases. I think people have gotten a bit too comfortable with the idea that the internet is a substitute for social functions in general.
