You are right if you are talking about specific parts of a video card like third-party video decoders and such.
And besides, optimizing a driver is not cheating. Intel is just not putting as much energy in optimizing the Linux drivers.
And what is wrong with placing a dirty hack in the driver you develop on your own? Practically speaking, nouveau was full of hacks since the developers were still figuring things out on how to handle it. After a big rewrite in the kernel, libdrm and mesa things are starting to look 'nice'. A very nice example is this commit (link!). It is a hack because it will not work under all states of the world. But it works!