Daniel Mackay is probably the worst example, Roddy McGregor and Cammy Harper are two that should have played more than they did, partly due to pressures on gaining promotion back to the top league and partly due to management persisting with average journeymen.
The pathway is there, it's the management teams call as to if and when the youth make it all the way.
If the management team had followed up on the investment of time & money at youth level, played a few of the youngsters on a weekly basis , we would probably be about the same position in the league...but possibly with more money to attract a top player who might have scored the goals to make a difference.
That's how the system should work.