I already pointed out that yes, the draw call overhead in OGL is less than D3D in Windows, because of how D3D runs almost entirely in a separate process (so there's extra context switches and IPC for every D3D call) for security and stability reasons while the GL drivers do not.
It's like comparing OpenGL on classic Mesa vs OpenGL on Gallium. You get totally different performance numbers even though they're both using the extra same frontend Mesa OpenGL code. You even see classic Mesa running faster, or with more features, or with more stability in some cases, even though Gallium is generally considered the superior backend.
Where things go in D3D's favor are the API requiring less overhead (and yes, this _is real_, which is specifically why NVIDIA created all those fancy NV_ extensions for bindless graphics and direct state access that aren't in OpenGL proper -- they really do make a difference!) and the case that the D3D drivers on Windows are usually of higher quality than their OGL counterparts simply because the drivers are tested and vetted by far more apps.