Oh no, rendering was never a bottle neck. I do postwork, scripting animations, writing, and editing while renders are running, and I also have renders running when working on my second job (which is a 50% work-from-home gig). I was never idling while waiting for renders, there's always so much other work to do in parallel while renders are happening.
The real time sink for this thing is preparing images for rendering (sets, lighting, poses, dforce and tweaking). That's (<pulls some number from thin air>) up to 80% of time spent, and that work still takes place for the most part on my old rig.
So, coming back to the apparent development speed increase: that has a lot more to do with the fact that there aren't all that many complex lewd interactions in this segment, which are always grueling affairs that may take up 100s of images in all kinds of variants of undressed and soiled states. And since preparing images is the largest time sink, and lewd scenes have so many, they take a long, long time to prepare images for. Especially the ones where more than two persons are interacting.
So, why the new hardware then? VRAM. For multi character scenes, fitting all textures in the GPU RAM is always a struggle, and going from 2x8 GB to a single 24 GB GPU that is not a problem anymore.
