The operating system used is not relevant here.
The operating system used is not relevant here.
Only a handful of games get perfect optimization (such as Left 4 Dead), but most will perform significantly better on Windows because the drivers are tailored for that system.
Windows 95 Microsoft introduced DirectX, now the standard for most contemporary game engines. Modern GPUs are designed for this support. Linux and OSX focus on Vulkan and OpenGL, which add more complexity and aren't ideal for current engines and games.
It's accurate that a 550 Ti is preferable to a 650M. While Rocket League performs better on Windows, especially with a hackintosh setup, that's not a solid comparison.