Not denying that the NRL is more competitive at all, it clearly is. Missed the top 5 statement/relevance so yeah, definitely wrong on that, other than Melbourne and Brisbane usually/mostly/more-often-than-not making the top 5. For what it is worth, it is also worth bearing in mind factors such as the NRL's shorter seasons and thus inconsistent ones, much moreso than in SL. Shorter seasons allow slightly more random results to surface, each individual match is worth more so the 'shocks' that happen make more impact on the table. Longer seasons will sort the rankings of teams more effeciently with respect to ability than shorter ones (whether or not changes in ability throughout a season is another matter factored into this I suppose).
The inconsistent fixture lists should also give an illusion of teams being able to rise and fall more each year. Imagine, say, Hull KR over here having to play Warrington, Wigan, St. Helens, Leeds, Huddersfield etc last year twice, and the weaker teams once, then the next year having double fixtures against Widnes, London and so on. They will do better the second year even if they don't get any better by virtue of the fixture list, there is an illusion of greater change. I'd say this factor will play some role in the apparent greater rises and falls year on year in the NRL, but I really cannot be bothered fetching the evidence, so Keith if you would be so kind? You seem to enjoy it
FWIW, the Superleague equivalent. To keep it relatively fair, it is on table position (so including point deductions etc). Furthermore, each are only by the seasons they competed in SL. Finally, the % is against the equivalent for a playoff in the NRL each year it contrasts with in the other % list. So since GC entered I'll count top half, when it was only 14 teams (2001) for 8 playoff places, top 6 still in SL etc etc...
St Helens - 100%
Leeds - 100%
Wigan - 82%
Bradford - 73%
Hull FC - 64%
Hull KR - 60%
Warrington - 55%
Huddersfield - 40%
Catalan - 33%
London - 27%
Castleford - 22%
Wakefield - 18%
Salford - 11%
Crusaders - 0%
Widnes - 0%
Leigh - 0%
Halifax - 0%
Relagation or new teams tend to live around the bottom, traditionally strong teams around the top. Not surprising at all really. Maybe the closed shop helps with competitiveness

or just the generally closer nature in financial power etc of the teams over there.