It's easy to look back and bring up Eriksen, Lamela, Rose, Walker, Lloris, Dembele and Kane as players who were already here when Poch arrived - but it's also silly to think Pochettino didn't improve at least half of that bunch.
Just go and look at the opening few pages of the Kane thread to see what everyone thought about him. Rose was getting horrible abuse on Twitter when Pochettino gave him a brand new deal in his first season here which made him delete it. Lamela was being written off as a flop already despite being injured in his first season and hardly getting a look in under AVB and Sherwood and Dembele and Walker were still ridiculously inconsistent, despite having the ability and Vertonghen was getting abused for "not caring" because of the way he was standing in a dugout. It wasn't even until Euro 2016 that people besides Spurs started to actually rate Kyle Walker as a player.
He still had a squad involving Naughton, Chiriches, Adebayor, Paulinho, Soldado, Holtby, Capoue, Townsend, Dawson, Sigurdsson, Carroll, Sandro, Lennon, Fryers. Which was HALF of our squad when he arrived.
That's a whole lot of shit.
Over half the squad last season was signed by Pochettino. Over half the squad the year before was signed by Pochettino (some would say 16/17 was our best season under him).