I agree with this. My preference is pretty slim and just based on my own experiences from having both brands. But it wouldn't stop me from recommending an Nvidia card if it made sense for the use case.
THere are TONS of use cases that directly corner you into Nvidia or AMD.
It's such a simple flow chart really someone should just write one out.
I'm cornered into AMD products currently based on my gaming habits/tastes.
Other users are cornered into Nvidia products.
I'd say though that most users are in the wrong freaking corner and are thus getting horrible value for their money.
Example would be like getting a R9 390x now and gaming on a 1080p TN monitor. When you could get a R9 390 + cheap Freesync monitor and vastly improve your experience.
In this example it's not even a brand bias, it's just not utilizing the money as efficiently as possible to improve your gaming experience.
That's really the problem here. People's brand bias hurts them from utilizing their money as efficiently as possible to further their goal.
Lack of knowledge of how technologies like VSR/DSR/Freesync/Gsync/etc. also hurts them.