So following your line of argument, these senior players aren't up to it.
Logically, we then need to question why they are still here. I have no doubt many of the players you have mentioned - Robertson, Green, Bruce - would have been worth something in a trade before now, but 'we' chose to keep these players.
If they are not good enough, who is responsible for keeping them here? To put it into perspective, ND had been MFC coach for a few years before Green debuted, and Robertson was ~19 when ND started at Melbourne.