Earlier quoted context omitted.
In practical terms it dilutes the value of 4 and 5 star reviews for other restaurants. There's some cognitive dissonance involved when McDonald's gets a 4.6/5 and a mom and pop haute-cuisine restaurant gets a 4.6/5 as well. These are two very different dining experiences but they are being judged using the same system and feels inaccurate.
For what McDonalds is they probably deliver a 5 star review the way their customers see it. You probably have to divide restaurants into different categories and compare within them. I beat a lot of people will rate MCDonalds higher than haute cuisine restaurants even in direct comparison. There is no absolute rating for restaurants.
But it should be a direct comparison, I certainly think KFC is far superior to most haute cuisine fried chicken.