But when NSW dominated Origin there was talk of it losing relevance.
I think in competitions like the Bledisloe or Origin, dominance by one team can be sustained whilst increasing the interest in it, but only if that dominance is by the team that started out as underdogs.
In Origin the whole point was to give a written off Qld side a fair crack, but people still expected them to get spanked. When NSW started dominating that early 00s period people started to go off it a bit, because NSW has half the NRL teams so it kinda seems like they should win Origin all the time. That they don't is what makes Qld's wins more dramatic.
In the Bledisloe it's a little different, but the principle is the same - the All Blacks had dominated Australia for decades until the 80s, only dropping rare series, so when Australia started winning it the underdog value of our wins and the development of a genuine rivalry generated great interest.
It's why when we won it 5 years in a row (well, retained it) interest was still sky high. But the All Blacks thumping us year after year is a little like the Kangaroos thumping the Kiwis in they way they once did - it just gets boring because there's no theatre to it - it's just what you expect to happen.