Unreal is older than Unity and you seem to have completely missed the point here.
For every difficult task the response some people get is “you have the source code!” as if it’s enough. Sure you have the source code but is the engine itself componentized enough to allow adding custom features? I doubt it! Why? Because it’s an old engine. It is why you have people asking for custom shader support in the Feedback forum section and much more.
As for calling those assets ****, I’m pretty sure UE4 users would love to have GI lighting, custom shaders and much more available to them.
As for your car sale, I’d definitely NOT buy the Chevrolet unless you told me there are shops I can replace parts.