I can find nothing wrong in waiting to give chances to a 18-19 years old youngster. Maybe SAF got it wrong regarding the time of him playing and that he proved he could have played earlier, ok but bring me one manager who would have thought an 18 years old player could be a starter at this time. If SAF with all his history with youngsters didn't, who would have ?
The point is he ended up leaving under SAF and the latter insulted Raiola on several occasions due to, so not sure about bringing a comparison for Mouinho vs SAF regarding Pogba treatment, because SAF wouldn't have even brought Pogba back because he would have never dealt with Raiola again, so let's leave this point aside imo.