Arte

Hello, @Springs
 
Your problem is independent of the program used to unpack to UV. The current UV tools included in Cinema 4D are very good and you complain about them unnecessarily.
 
Your problem lies elsewhere. It all depends on how you create models with reduced mesh size. You can do this in two ways:
You create successive LOD models based on the former with the greatest number of polygons. You create each LOD model from scratch. In general, the right workflow should be based on step 1, but there are also occasions when it is better to do something new, which is according to point 2.
 
Proceed as in point 1:
After you finish modeling the object with the highest accuracy, you should map (all its elements) UV. Then you need to apply a color texture to control detail placement. The next model is obtained by reducing the higher model. You can do it manually. When you carefully remove consecutive model edges, the UV mapping is mostly preserved. Occasionally the UV mapping may break somewhere, however this can usually be quickly and easily repaired by welding the UV dots or edges. You can also use the Polygon Reduction Generator - during the reduction, if you check the "Keep UV limits" check box, the UV mapping will remain unchanged. Finally, you make corrections to the mesh, remove unnecessary edges or add new ones. When adding, the UV mapping is preserved. Finally, you correct the broken spots in UV.  
Proceeding as in point 2.
Here you do everything from scratch. Usually it concerns small elements that are easier to make new (e.g. cubes, spheres) than to reduce the mesh. You need to do a new UV mapping. When doing UV mapping from scratch, most often you have to fit into an existing texture. There are cases where the texture for the next LOD must be new. But usually a basic one is used, only the game engine automatically reduces its resolution  
In summary, the problem is not with UV unpacking, but with how to reduce the model mesh. Regardless of the method, however, manual UV enhancement work is inevitable. To do this automatically and simultaneously with a beautiful mesh and correct UV, advanced artificial intelligence algorithms would have to be developed. I have not seen such algorithms yet that would do it wonderfully, there is always some "but". But what's there (such as "Polygon Reduction", for example, also give a lot of help.
 
Below is an example of the "Polygon Reduction" tool. You can see reduced polygons and preserved UV mapping.
 

 

Hi
If you do not have an active license, the license management window will open when you launch Cinema 4D. You must have the "My MAXON" tab active (1). By default, the "Status" (2) content is shown.
You must now click the "Licenses" tab (3). Then release the license by clicking "Release" (4). Click "Status" again (2).
Finally, click in "OK" (5). And that's all. 🙂