Do you know that this is a team with many different skill sets, like pretty much every game team? Most people on the team can't fix FPS issues, so they do spent their time working on their "stupid" stuff.
FPS issues don't have an "I Win" button you can press to make it all better. It takes lots of time to analyze performance and find bottlenecks, which then often have no easy fix, but to rewrite and retest something, which often results in minimal gains. Features have maximum limits at which they can be optimized to run.
I've actually been spending half my time the last few weeks doing that and cleaning up the project of old/unused files. For example, I found an old unneeded water depth camera, that was rendering nothing each frame. After time spend researching it, removing and testing, I saw a 3% FPS gain. Not much. Path grid updates have also been optimized, which is not something increasing overall FPS, but reduces frame spikes. Terrain shader has been updated for good gains. Tree batching/instancing is being analyzed and tweaked. To get large gains, you have to do that over and over on many systems. Today I started moving many of those improvements to 19.2 for testing, so the next exp will have them.
