Yeah I agree on that. Wherever the issue is, I don't think it has anything to do with the algorithmic planet generation, as framerates are usually plenty stable when in the middle of nowhere on a planet. I can get 75fps even at native resolution there.
It's settlements that's the issue, and I can't quite figure out what exactly the CPU is doing there considering there's not really all THAT much going on there besides some basic AI pathing (assuming the settlement isn't on high alert) and you aren't covering all that much ground for the terrain generation to be taking up that many cycles. It's just...mystifying.
I think its the efficiency of the rendering pipeline and loading in resources on demand, its code and is either architected poorly or just poorly optimized.
I notice distinct stutters as I get close to a settlement, and when I move around and look in different areas. Its trying to load up the assets and render everything on-demand but they can't really subdivide the area logically easily to isolate how much they have to render in a single frame. Most of the settlement buildings have windows and its difficult for them to know if you can see inside those windows, even if they are on the other side of the building and you can get in trouble I think if you start trying to chop things up like that.
Some games like Doom 3 (I use this because thats the last time I did any level design etc in a game) had something called visportals and you used them to segment a map such that as long as you were on 1 side of say 2 portals (think windows lined up such that from 1 perspective there is some geometry preventing you from seeing through both windows at the same time) they would not load anything on the far side of the portals. You could use a hallway for example to isolate areas by having a 90 degree bend with a visportal in both hallways but until you enter portal 1, nothing past portal 2 would load. When you were in front of portal 1 it would load everything between portal 1 and 2, when you entered portal 1 it loaded the stuff past portal 2 even though you couldn't see it yet (ie you didn't round the corner yet).
Windows break this portaling type tricks so you have to either load everything in the whole settlement basically at once or, like they seem to be doing, take an approach where until you look in a direction or get close enough to a building, they don't load and render the stuff inside. If you have enough VRAM you can probably handle having the whole settlement loaded into VRAM, along with all textures and if your card is fast enough can render everything at a high frame rate. Once I've visited most/all of the settlement, I stop getting framerate drops.
I think they are "lazy loading" resources and geometry such that when you turn in a direction that you've not looked before at a closeish range (LOD having an impact here, if you are far enough away from a window I think they can safely say you can't see inside) they are having to do a bunch of stuff at once, stalling the rendering pipeline until the geometry etc is loaded into VRAM and can then be rendered, even for stuff you might not actually be able to see with the naked eye. The rendering pipeline is blocking and real time though, so each frame has to go through a bunch of different passes and sent to the monitor in a single-threaded way (more or less), and it doesn't take much to stall it unless you are way overpowered or have much lower settings.
The fixes will probably involve a) more intelligent asset loading where they better predict what you'll need and eager-load stuff onto hardware that can handle say the whole settlement geometry and textures, b) better multithreading where they are loading in resources before you need them in the background without stalling the pipeline, c) more tweaks to how settlements are divided up so that they can better tell when they need to load in resources (ie for lower end cards that definitely can't handle the whole thing).
I think c) is the hardest because the settlements are already generated and potentially are randomized. With scoped weapons its gonna be tough to tell if the player can see what windows and whether to render whats inside this building or that. Hopefully they can get most of the whole settlement in memory and then have ways to use LOD better to keep up the rendering speed such that you keep a good frame rate even if you lose some details in the distance (having fog/dust can help with that by hiding the fact that they aren't rendering long distance stuff as cleanly).
The settlements themselves are not bigger or more complex than most FPS games but the lack of hallways and especially all the windows definitely makes this more of a challenge so I can sympathize with the developers that its a more difficult challenge than it might seem but I think they unfortunately coded it in such a way that top end hardware doesn't get utilized that much better than lower end, they ended up creating a not-great experience for everyone across the board.
