Rafinha has always been his personal experiment dating back to Celta. He came back from Celta with Rafinha in tow as one of his favorite players already and the Alcanatara brother counts as much for Lucho giving La Masia a chance as it does with Iniesta or Pique. Roberto being forced into the RB spot is a prime example of not trusting La Masia at all, we have other players who can play RB, but they're not first team players. And Denis was on loan for 2 seasons and only spent a single season with the B team, he's more of an experienced La Liga purchase than a La Masia promotion.
Munir doesn't have to prove Lucho wrong with Valencia, it's a fact that he was better when he left, than Paco is now, and that's even with him constantly being played out of position, something Paco arbitrarily has not had to deal with even a single time since signing here. Grimaldo is a similar case, whether he proves Lucho wrong or not, sheer stubbornness and stupidity is the only explanation for why Lucho would rather lose games with Adriano/Mathieu at LB, than so much as give Grimaldo minutes in friendlies or dead games, to see how he'd do. Same thing applies to the likes of Nilli and Palencia, even as we speak. Even the likes of Marlon and Tarin are lucky to get a sniff of action despite 2 of our aging CBs (Mascherano and Mathieu) being likely to leave this summer. And this is not even mentioning Alena rarely getting any minutes or Samper getting shipped off, and Gomes is proof that how "ready" they are isn't an actual metric to Lucho.
Bringing up obvious failed players like Adama and Deulofeu is just a strawman argument as far as I'm concerned. Yes it's possible Lucho made some right decisions in choosing to ignore some players but I'd say players like Deulofeu are exactly what is needed in a team that relies so heavily on a single trio of players, although that really is straying away from the original point. Him ignoring idiots who only know how to dribble doesn't mean that he's justified in all of his other decisions concerning the Cantera.