While Bennett will go down as one of the greatest coaches, he has had some pretty good rosters to work with. The Broncos of the 90s were stacked with SOO and international players, the Dragon's were regular semi final contenders and he put the finishing touches to it.
The age old question of does a coach make a team or does a team make a coach I don't think will ever be answered as top line coaches generally won't go to bottom feeder teams and tarnish their reputations. It would be nice to see a Bellamy, Robinson or Bennett go to say a Warriors or Tigers or the Dragons and see if they can get them to contend regularly with the squads they have but unlikely to happen.