d3dcompiler_XX.dll and opengl32sw.dll are not included in the Windows Python wheels.
Due to dynamic OpengGL leading if OpenGL >=2.0 is not available Qt will try ANGLE.
ANGLE requires three DLL files
- libEGL.dll (included)
- libGLESv2.dll (included)
- d3dcompiler_XX.dll (not included)
d3dcompiler_XX.dll is the DirectX shader compiler, "where XX is the version number that ANGLE (libGLESv2) was linked against." 
If OpenGL >= 2.0 is not available and ANGLE is not available Qt will fallback to a software renderer.
This requires opengl32sw.dll  which is not included in the wheel.