Sixth generation graphics? (Like gamecube.)

I’m still pretty new to graphics, mainly lighting.

Most games of that generation used only diffuse (color) maps within their materials. (No normal maps, no roughness, specular, etc.)

Only a few objects actually follow some light logic, such as the characters in the above image.
But even the metallic highlights on Fludd were faked with diffuse.

Most of the shading is completely static, and looks the same from every angle. There seems to be no fresnel, etc.

So how can I recreate this style in UE4? And would it look correct, or unfitting in this engine? About how much of a performance saver would it be? (Not including the lower res and poly count of that time.)

Did you ever find an answer to this? I’m really curious.