What are you talking about? You could point to hundreds of Minor Leaguers who had great numbers in AA or AAA and didn't do anything in the Pros.
Peacock or anyone else is no different. Scouts are not deriding his stuff. Guys like Kevin Goldstein just said a few days ago that he has two true plus pitches (fastball, slider). Goldstein says he is a big fan. Others will soon hop on board.
For the record, I'm not knocking on Peacock - I'm knocking SF's tireless defense of him.