He is correct tho. De Ceglie loan to Siena from our youth team is reason why he became a Senior team player coming back. Similar for Marchisio and Giovinco in Empoli. Or Fagioli in Cremonese recently. Coming back to parent club with full season on loan as starter gives you new status.
Tho with U23 next gen team now the hurdle between youth player to senior team is much easier. So in that Miretti and other youth players are better off. It's not go out loan were you likely to be dissappear as trade piece, or be ignored in youth teams if you stay etc.
Also the question is does someone like Miretti even need loan for playing time besides just generally needing confidence boost. Because Miretti played 50 Juve games before even turning 20. That's much more then any Juve youth product in past I think. Kean debuted at 16, but he was used sparingly and was loaned out too.