Well, this the price you pay for automated unwrapping.
While it workd for some meshes quite well, usually models like this tend to produce clutter, as shown in your screenshot.
I think the automatic lightmap generation tool in UE is sufficient enough for a quick build.
When it comes to creating the game-ready lightmaps for the mesh, there is no way around crwating them in a 3d application.
There you can manually create the lightmaps and also scalethe islands according to importance. The underside of the chair needs probably less resolution than the top side, etc.
That is something no automatd too can ever achieve because it does not know your intentions with the mesh and its plecment scenarios.
If you create th UV maps in a regular 3D modelling application, you can add multiple UV channels for textures and lightmaps.
I guess you seek for a way around the time consuming unwrapping. But there is no way around it…
Only 1000 …pff
PPS: Actually, I know one. No joke… The (automated) unwrapping tools from MODO are just awesome. !!