The point of discussion isn't to create some sort of internet that might one day be studied and determined to contain useful information, the point of discussion is that those who participate can learn and improve. Sometimes this necessitates saying things that have already been said. That's not a problem.
As for the notion that sometimes discussing things with people in significantly different circumstances to yourself might not be the highest value discussion you could have, I agree. However it's still fun, interesting, etc. Better use of time than Netflix, that's for sure.
It feels like a weak point. Maybe the best insights are written by professional writers, for example. In such a case there's no loss from industrial self-censorship.
On the other hand, it is true that successful startup founders usually leveraged some deep insight to grow fast and profit. But those insights have been "tapped out", so to speak, therefore are not really useful anymore. They were valuable for the founders but the value is non-transferable.
In my case, I'm writing mostly to become a better writer/communicator, so it doesn't particularly matter if I convey useful/valuable information or if it gets discussed; the aim is to do it clearly in a short amount of time. It's a different calculation for a person with children and a demanding job.