That’s not what those are about, first one you can bet they have optimized their assets for the engine. Second one has absolutely nothing to do with UE4, that’s a DX12 demo for technology used in the Final Fantasy 15 engine which is not UE4, not only that, it’s running on 4 graphics cards. DX12 in UE4 is an experimental feature and probably won’t do what you’re expecting. If’s fine you’re wanting to do something the engine isn’t really capable of, and surely they’ll want to improve things, but for now you’ll have to use the tools in the way they’re designed.