So you know founders that went through YC and don't feel like they got much out of it? I wouldn't want you to break any confidences, but I'd be interested in hearing more such folks and what they think of YC.
If you think about it, the worst case for a company that goes through yc is that it's neutral. They can't really hurt anything — when companies fail (or struggle) it's never because of yc. There are hundreds of reasons companies fail.
So the tl;dr; is that people probably won't ever say "yc was bad for us", and companies that come out doing well won't think "yc wasn't great for us".
First thought is that if pretty experienced founders who are starting a company in a space YC isn't experienced in(e.g. biotech 5 years ago) went through it they might not get much out of it.