I tend to think it's not so much the quality of half, but the expectation clubs have for their halves..everyone wants a game breaker, everyone plays to a similar mould, there's been a bit of a lack of innovation from the bottom clubs which means they keep cycling through halves looking for a magic bullet, rather than developing their squad and style.
I'm such a huge fan of Canberra over the last 3-5 seasons for that reason, being able to get results from halves like Sezer, Wighton (before he really 'got' his 5/8 game last year) and now G Williams whose developed a really unusual style comes out of being clever with half usage imo.
Game's evolving again, the ball playing lock is back from the dead against all odds, fullbacks has to be 5/8's for five or ten years and I think we're seeing a bit of a flexibility in that now that the block plays and tip ons are being too easily defended.
I agree there are a lack of Thurston/Cronk quality 7's, but there's also a lack of Smith quality hookers, Tedesco quality fullbacks, etc... The dud clubs gotta think outside the box like Canberra did to get up in the top 4