We have a lot of people working on a lot of stuff. It was never the "main" focus. It is an ongoing priority for a few of us. I've spent a good amount of time optimizing stuff over the last 6 months (for A17 and A18), but not exclusively since there are many bugs to be fixed and features to improve or add.
Case in point:
SSR effect is very demanding on GPU, which you could not turn off in A17 until 17.3 (using a console command). 17.4 now has a video option to disable it.
The SSR effect actually has a variety of values. I tested various combinations this week and A18 now has Low, Medium and High SSR settings. These have about 25%, 45% and 90% of the overhead of A17's SSR.