Theres a huge difference between not coming through and disappearing off the face of the earth.
No expectation - Harper (the kid from Madrid) was given a huge fanfare when he arrived, but he can't even get in the DS team any more, he is always on the bench. Hambo (the Finish Zlatan) hasn't kicked a ball in a year. Roland Bergkamp - they were selling shirts in the club shop with his name on the back!!!!! There was huge expectation from these players alone.
Akindayini, Maksimenko, Fenelon etc... the list is endless. The only players that make it are the ones who rarely played for the DS and were chucked in to the first team, Goldson and Ince. Anyone that plays more than a couple of games goes backwards.
The point was that at least Manu made the first team and got on the scoresheet, so can't be classed as big a failure as the players above, in my opinion.
Manu was signed for the first team. All the other plywrs listed are gambles for the future. The amount of young players who make it is a tiny. However a lot of ds players now have played proffessionally. Rea, kasim, rodgers, Bradley Barry, dickenson and barker to name the first few off the top and f my head, as well as March, JFC and Ince as well as Walton. So to see these signimgs as a failure shows your lack of understanding as to what the DS is meant for.