The lighting and volumetric atmospherics are extremely nice and top draw tech wise, especially at this scale which from a technology point of view is a massive achievement.
That is really difficult stuff and requires top draw talent, they have done that.
Foliage assets and textures are old and very much last gen, that is actually easy to improve, you just use the latest tools and techniques to make better ones, not at all difficult, just time consuming, that includes making better water bodies. for trees, bushes ecte.... use the latest version of Speedtree to redo those assets, for example.
The real problem is visible good quality dense foliage at this scale, that #### is really hard because while its easy just to make a massive forest with a million high quality trees the GPU just cannot render that level of detail at reasonable frame rates, so you have to optimise it at scale, that means using very low quality assets like 2D cards at the longest distance and LOD sets that get progressively more detailed as the camera gets closer and there is less of it on screen, that causes that visual "pop in" that you see, you can see it clearly in the Star Engine demo.
Epic Games have created a solution to it by creating an algorithm that dynamically changes the tessellation values of the asset as the camera moves around, it does away with LOD's completely and its very effective, it cracks that problem, Its called Nanite and its been available since Unreal Engine 5.
CIG need to make their own version of it.
PS: that assets pop in also causes stutter, because its quite an abrupt thing for the GPU to handle when new assets suddenly pop in on screen at scale, its sudden demands of the GPU popping in big chunks at scale that makes it choppy, its sudden peaks and troth's in frame rates when you're flying low at high speed. Again Nanite would fix that.