I think, you're getting caught up with he hype machine. No top level club can realistically expect three or four players of one particular youth set up to step up to the first team. Take one look at our (or that of any top team's) squad and you'll find that majority of players in it are bought post the age of 18 and were options for the first team from the moment they were bought.
Every year there is a hype about three or four players. It is probably because games played by these players are accessible to many of us and our proximity to these players (and lack of knowledge about others of the same age group) makes us feel they are better than what they are. It is the lottery ticket buyer's syndrome. Since, the positive scenario of winning the lottery goes through one's mind, a lottery ticket buyer will always over-estimate the probability of him/her winning the lottery. (If he doesn't he won't buy the ticket)
Personally, I never expected JET or Eisfeld or Olsson to realistically step up. Look at the players who have made it successfully at Arsenal in the past few years from the youth set up - Cesc, Song, Jack, Gibbs, Ramsey, Ox. Cesc, Jack, Ramsey and Ox were special talents who could actually make a difference in the first team right from the age of 17 - something none of our failed players did. The only two exceptions here are Song and Gibbs. However, they have turned into seemingly successful players from a wide bunch who were all promising (Denilson, Djourou, Bendtner, JET, Lansbury, Bartley, Vela, Coquelin etc etc), so, that tells you the probability of success of players who are not clearly special, but, have shown enough to prove that they might have a Premier League or Championship level career.
Basically, if a player is only Olsson, Bellerin or Eisfeld good, you count him out. Afobe and Aneke were hyped up a year or two ago and both seem to have ended up at nought. I'd put Akpom, Ryp and Gnabry at an advanced level where they seem set to make it at one of the top divisions, but, may not be clear-cut Arsenal players. It'd be good if one of the aforementioned five makes it at Arsenal, but, I certainly wouldn't be betting my money on any of them.
Zelalem, touch wood, seems to be the only one in the Cesc/Jack/Ox/Ramsey level. But, we'll get to know more about him at the Capital One Cup, this year.