I agree that mostly every graphics technique used in modern AAA game engines has been discovered by researchers and is present in published academic papers. However, when implementing something like physically based shading, the equations and algorithms can be got for papers but there are a lot of choices to be made on how to actually implement it. This is where the engineering comes in. Its not just about implementing one feature efficiently but also integrating numerous features efficiently. When you look at what a rendering engine does, there are a lot of things that can go wrong. It is responsible for handling rigid and skeletal meshes, materials, skinning for skeletal animations, deferred and forward lighting, shadow mapping, ambient occlusion, frustum culling, occlusion culling, screen space particles, multi-threading, instancing, transparency, translucency and many different post processing effects such as blur. These elements can be implemented one by one but implementing them optimally takes a huge amount of time. Time does seem to be the issue here and this is only the graphics engine. For that reason, I will probably use UE4 and modify it if necessary.