The point is that the current manager and previous managers have all deemed he is not good enough/ready! I am not sure of Mathius judgement either on promoting young players. The Hughes episode put me off - if Hughes had more senior players around him like Turnbull and Pierre he might have made a more favourable impression.
You definitely need a mix. I wouldn't advocate wholesale changes and putting young players under that much pressure. I think we were right to sign a number of the 2nd years but their progression to 1st team has to be carefully managed.