I don't actually care, how many we keep. It would be preferable to have a core of homegrown players but the rate at which we discard them is making that very unlikely. But I only care how many get a decent opportunity, to be the best they can whilst at City & have a fair test to see if they can make it. That has rarely happened.
There are two arguments which generally come up, mainly from those who don't really car about the subject but like to argue the toss anyhow. 1: 'If they are good enough, they will make it, no need to worry about it' (which usually has added: 'so & so is doing nothing at Barnstoneworth Utd since he left & if he was any good, he would have been outstanding there' which is just proof of complete ignorance of the subject by the posters involved).
2: 'Teams at City's level can't afford be starting kids every week (which nobody has EVER, EVER asked for them to do & is probably true) & this is usually followed with 'teams who win trophies don't bring through kids' which is the absolute opposite of the truth.
There is no risk & no problem, with getting kids involved in the first team squad, if they are talented kids. Most of the kids we have had, over the last ten years or more, are talented, some incredibly so. The problem would come, if those kids have to replace, for example Aguero or John Stones regularly, which, as you point out, they don't.
So we are left with the ideal situation: a squad full of brilliant players, a team which wins most matches & a shitload of games to play.
So that allows us to give Demichelis or Navas, an extra runout when we are 3-0 up.
That's the message we send out, for years. Then we wonder why Sancho fucks off when his contact runs out.