Mourinho isn't exactly famed for promoting youth...
If anything Rafa (even as interim manager) did more for the youth here, gave Ake some games (tried Piazon in a league game v Villa and RDM played Piazon in the C1 Cup).
Wilshere is only a couple of years elder than McEachran....... (hard to imagine)
I don't see how promoting youth sacrifices trophies, even a major club full of superstars like Real Madrid plays some of its younger players (Jese, Casmeiro, Morata etc does Illaramendi count?). Barcelona manage to give younger players chances in their 1st team every now and then (they started Cuenca in a semi-final against us). Bayern also have a successful youth academy (Muller, Schweinsteiger, Lahm). Borussia Dortmund have always encouraged their younger players. Arsenal played young Miyachi against us have tried to integrate Serge Gnabry into the side (and have a reputation for always encouraging youth). So how does bringing youth players make you weaker?