In my opinion, they were unfair since you could have a great relationship with a boss over the years, then end up working for another one who was a total jerk, which was reflected in his evaluation of you.
We went through a similar period at my work place.
The executives had a given budget for raises and had to justify the raises employees got in there performance reviews.
What happened is that favored employees got good raises and everyone else got minimums.
So, if your supervisor didn’t like you for being outspoken but you were a good performer you still got a poor review rating.
No appeal process of course. Put up with it or find a new job.