Comment by bayindirh

A friend of mine developed his own game engine, and what he said is you need to bargain with the nVidia driver, because hardware doesn't perform at its peak when you write everything honoring the spec, and driver feels free to ignore your commands about how you want to do some things (e.g. memory transfers).

Like board manufacturers, the game developers also need to please the drivers and do the way driver silently dictates to them (regardless of what DirectX, OpenGL or Vulkan says), otherwise all bets are off.