Trent wouldn't get a chance to play under Allegri, if Juventus would have signed someone like Robertson, Henderson, Matip you'd be crying that we are buying a shitty players.
Hell, Klopp was able to turn Schmelzer, Piszcek and Grosskruetz into world class fullbacks and you telling me that Pellegrini wouldn't have a chance to succeed under Klopp ? Nonsense. And the list goes on - Kagawa, Gotze, Blazscykowski, Piszcek Lewandowski, Gundogan, Mkhitaryan, Aubameyang etc. Etc. so many players are improved a lot and have played above their level under Klopp's guidance.