The better the game, the longer it takes to create worthwhile content.
Not true.
First of all, its a matter of taste. So your little rule here is untrue just on the face of it.
I for example struggle to stay engaged with an AVN after 6 months of Dev time.
Once it hits 9 months+ of Dev time I will almost certainly quit even if I really love the story, which I did with Genex Love.
Theres an AVN called 'Crimson High' it usually has a Dev cycle of roughly 6 weeks. Its one of the best AVN I have ever read.