I think we could find reasons for some teams to be having success, where others do not. But first, let us take a
look at the play by play against Canberra for the Broncos. Within the first 20 min there were 6 penalties or 6-agains against the Broncos vs 1 against raiders. This amounts to hard defensive work early. Raiders have more energy to attack, Broncos lose more early. The result is similar to running hill-sprints at the start of a Marathon. Broncos didn't help themselves by holding the ball when they had it, but psychologically it's the same old story for Broncos players.
It might be argued that they only have themselves to blame, but when it happens every week, it becomes less likely. Against the Roosters it was not the case and we beat them.
Raiders aren't that good a side, that's true, but if they were not given so much early ball, the game would not have been a blowout.
To your point about other teams: this is actually an aid to the targeting argument against the Broncos as you are seeing a fair representation of the quality of the teams with some bad reffing and some good reffing and less psychological effects.
Melbourne will continue to do well, because the NRL needs a strong team in AFL heartland. Cronulla conveniently won a Premiership in the one year they weren't cheating, just as their club was floundering financially and on the brink of collapse.
You are right, we aren't used to being shit because we have always had first pick of the bunch of good QLD talent, and we still do. But now a new Brisbane team is planned and all of a sudden Broncos turn to shit? When the Titans started they struggled for fans, they still do to an extent, but success helps. Similarly the Crushers, they could never compete with the Broncos when they came to join. They collapsed.
edit:
In the end, the NRL is a business. It was inevitable that it would turn out like this. It just took the Broncos losing like this for me to realise that.