One thing about you cannot ever compare UE to Unigine is that you have to be big corporation or just a millionaire to access their source if something needs modifications in core level. Thankfully Unreal is so accessible to everyone that even schools consider Unreal as a part of PC classes in future in my near town that i heard. Yes Unreal should be more modular in every aspect, from installation of components to cooking level of components and even when building whole engine.
NB, English is not my native language.