There are some basic things broken in the graphics engine: 1) Turning vsync "on" doesn't have the intended effect. There's still very visible tearing half way down the screen. 2) Turning vsync on in combination with full-screen mode results in a hideous stuttering when turning the viewport with the mouse. It looks like you got the swap chain sequence.. backwards? As in... swapping the "most recent" frame.. and then a…
>Test, test, test! Plug in multiple monitors. With different resolutions. Drag your game around between them. Try laptops with hybrid (NVIDIA+Intel) GPUs. Use a HDR monitor. Use one of those laptops with a hybrid card and unplug the power while your game is running. Plug the power back in. Change your desktop resolution while your game is running. Try to get 10-bit working. Try to get the game to look identical even on wide-gamut monitors. Etc..."
Some good feedback, but remember they're using Unity, so they're not directly controlling anything on a low level.
As for the 2nd part, this is really hard in a small team. For example I'm a solo dev, so I only have access to 2 monitors, 2 graphics cards etc. BUT there are paid for services that provide testing, although that costs money; so when they've made a bit of cash and have a bigger user base then they can probably afford those.