I think Unreal Engine has great menu systems, save game systems, and networking systems.
It doesn’t have the specific GUI for those systems; that’s left for you to fill in.
I also think Unreal Engine has great character animation systems, but doesn’t contain actual character meshes/animations, because those are also for you to fill in.
If you think your game would be fine with the blue (or white?) default Unreal mannequin, then perhaps there could also be various GUI screens for the things you mention, that would be as useful to a final game as the blue mannequin is – that is, not very.
Would the engine really be any better if that content was included? Do you use the included orange chairs in your game, too?