Having been playing AOS Since before the GHB, I have always felt the introduction of the GHB was what started the spiral into a lack of balance.
Prior to the GHB you tended to see ppl build lists more around what was cool and fun vs what was the most powerful. I mostly believe this was the case because there was no points system but the most ppl used the pool system which allowed for greater flexibility in army builds.
Once points and artifacts , traits, etc got introduced the game quickly became more about List Building than what was a cool looking army. And that's OK. It just a change but one that GW has not handled well IMO. They just have too many combinations out there and so many things are unused because a couple are so good.
From my perspective GW prefers the game to be about list building the strongest list (regardless of what they say with the 3 ways to play, its lip service) nowadays. I'd love to see them keep the optional stuff and switch from a direct point system to more of a pool to increase greater army variety