The obvious response would be Semaglutide which is a glucagon like peptide (GLP-1)

Well yes but that actually is well studied and known-safe, as much as we can know something still relatively newish to be safe.

The obvious response is the mass-market success of a drug that was approved by the traditional approval process? And in fact didn't even achieve mass market use until it was approved specifically for weightloss?

That's as far as you can get from "grey market."

They are in wide use outside of that community

No they're not lol.

Put some numerical values to "wide" please, so we can establish whether we mean the same thing by it.

I would be shocked to hear that more than 1% of Americans are using "grey market peptides," and I would be more shocked to hear that <1% usage is considered "wide" in anyone's book.

Even just grey market glps have millions of users. I'm not going to argue the definition of wide use. My point is that it's not just body builders. I hear people talking about peps at the barber and at cafes

Body builders are certainly on the forefront of biohacking, but the market is only getting bigger. Peptides are becoming popular in the same way that lifestyle HRT and tanning beds and plastic surgery and nutritional supplements are popular.