The last research I read said there are 1,500,000 kids playing youth football and the likelihood is 180 of them will reach a level where they play in the PL. 0.012%.
In 2016 the top 6 teams used 17 players from their academies.
In that context I don't think we do too badly? Many of the players go on to be sold and every now and again you get a world class player who goes for mega millions. Do you think all these clubs would do it if they didn't feel they got value for money? You don't get eg 3 a year, sometimes it's more sometimes it's none. If Spurs sell Kane how many years academy expenses will that pay?