They didn't have to be top quality to compete (and save us a ton of money) with the likes of Sissoko, Aurier, Nkoudou, Njie, Moura, Foyth, Sanchez, Bergwijn did they ? Surely that's the point. Use the academy to fill the squad roles for free (money and HG) and use the money to buy better quality players, not ones that are barely better than the academy ones you have already for free.
And players like Onomah, KWP had their development ruined by Pochettino - they missed out on playing proper football for 3 years and a crucial stage. This kids might not ultimately be good enough for a top 4 team, but neither are the likes of Sissoko, Aurier, Moura etc, that's we aren't a top 4 team anymore.
To put it brief, we hindered the progress of average kids (who could have become good) in order to buy average (and vastly overpriced) players from the outside.