Unreal 5 isn't about scans. Nanite means you don't have "lowpoly" geometry anymore. Scans are a quick way to get hipoly geometry for this type of environment but there's plenty of assets in the Unreal demo level that aren't scans. You can scan a gun but it generally will look a bit worse than a good subdivision surface…
Unreal 4.27 is also good if you're trying to do something non-photoreal and stylised. There's no point having the latest and greatest lighting system if you're just going to ignore it.
5.1 solved some problems with noise, interiors, and GI in general. Also, reflective and translucent materials look right now. Nanite works with thin meshes like tree leaves and even improves performance. All improvements are in "Unreal Sensei" channel video about UE5.1 changes.