Bellamy is pretty clearly the best in the business, and they've certainly got lucky or else they are very very good judges of cattle (or both) with some of the players they've brought in during their 21 seasons, and particularly under Bellamy. I think they reached their peak last year and are now on the way down. They were lucky to get such a banged up Sharks side.
The Roosters are different. Robbo is obviously a good coach, he's poised to win his second comp next week, so he must have something going for him, but it's some side he's got there, as it also was in 2013 when they were able to bring in SBW. I don't suggest they are cheating, what I think they are doing is legal but shouldn't be. It involves regularly having years like 2009 and 2016.
There's also the calls, which all year have favoured both of these sides. Why there is felt to be a need to do this is completely beyond me.