Utd signed Pogba when he was 16 years old? You can hardly class him as a product of Utd's academy.
As for the general point regarding City's academy. It's a very similar story to what we've seen at Chelsea. Both clubs invested massive amounts in their academy but it takes years for that investment to pay-off. City's Etihad campus opened less than 6 years ago - it's only going to be kids reaching 17-18 in the last couple of years that would have really benefited from City's investment in their academy and in that time they've produced two of the most exciting talents in the country.
I've no doubt that City's academy have got several Williams, Lingard, McTominay, Mensah, Tuanzebe's of this world too but because of the finances at City and the approach from the ownership, it's always going to be harder for these players to break through. City want immediate success and have the finances in place that allow them to sign tried and tested players, rather than take chances on prospects. Your Utd's and Liverpool's don't want to go out and sign squad players if they feel they can get 90% of the output from an academy player. Money is no object for City so why risk it when they can sign a safe option in Delph, Mahrez or Ake?
On the point about academies making money. The primary focus will always be to develop players for your side but I'm sure clubs have one eye on the business side of things too. You're lucky if you can bring through a player every 2-3 years that's good enough to be a squad player at a side that's aim is to challenge for the League and if you can get a genuine first team player every 10 years you've done well. Whether it's your Chelsea's and City's or your Liverpool's and Utd's, all these sides are handing out contracts to 16, 17 an 18 year olds that they know will never make it in their first team and that's because they hope they can sell them for £3-4m a few years down the line.