I don't think we have a problem with how we blood young blokes at all. The system is pretty clear: Promote from u20's to NSW cup, play a few games and then back to u20's. Promote NSW to first grade, play a few games and then back to NSW cup. Rinse and repeat with the stay at the higher level a bit longer each time. The player gets a taste of how hard it is to compete at the higher level and then just as they are getting physically tired, they get a spell back at the lower grade. It's a great way to do it.
I agree we have not managed this well in the past with Austin, Moylan and Graham good examples of this. Do it too fast and you break their bodies (subject to individual physical characteristics - Cartwright, Yeo and RGC are huge and can cope a bit better than a lightweight, like a 19 year old Moylan), too slow and you limit their development. Moylan is an example of this.
But there is no point in focussing on the past failures. We have a different management team now and they seem to be doing things the right way. There will always be disagreement over what players are good enough, that won't ever change. We can't keep them all.
As for playing Cartwright, he has played in halves in the juniors a number of times, there was no reason not to try him. Half the team was in Nepean getting treatment. It was great for him to get experience ball playing at the senior level. Could we have played better with say Peachey or Will Smith there? Possibly, we will never know, but we didn't lose the game because of him.