The goal of COTY is to pick the best car, compared to its peers. Not compare the finalists to each other.
Now, that is all well and good, but it is impossible for a person to be totally unbiased. Picture yourself as a motoring journalist. You are lucky enough to sample most of the finest cars in the market all year. Personally, I can say that once I have driven a car of a certain performance and luxury, anything less feels so inferior.
Now take this mindset into a mixture of cars from entry lever up to R1 million plus. Can you REALLY be objective enough after driving a Porsche and an M4 and then get in an A3 or a Citroen and go "hmmm, this A3 is better than the Merc A Class but not as good as the Macan is better than the Range Rover". No, you can't.
So the halo effects makes you pick the Porsche.
COTY is pointless to the average person. There really needs to be a COTY for normal people, and then a money no object COTY.
You can't possibly say that a Macan is better than its peers more than an A3 is better than its peers unless you are a savant or a robot.