In reality, it's missing as much as Unity or Unreal in that you still need to create your assets somewhere else, such as in a 2D paint program, like Photoshop, or a 3D modeling app, like 3DS Max.
I actually doubt that engines can provide better modelling/painting tools that other products such as 3DS Max or blender that specialize in these areas. So in that regard, I prefer to use external programs to do these jobs.
What I do think, however, is that the easier you can import these assets and get them working, the better.
Also, by "lightweight" I didn't mean a lack of features, but something that isn't as bulky and stubborn as unreal. Like having the option to only use minimal features and create a small application / extend on it with your own stuff.
