Most rates are personal opinion, something that can be decent as 5/10, some people might give it 2/10 because they just think its that bad.
Rate depends on the nature of the pokemon and IV (Mainly att/spatt, and speed, unless it is meant for defensive.) For example, you got a pikachu with 28 spatt and 25 spd with a timid nature, this would be good for a pikachu who uses spatt, but someone might give it a low rating because either they think a physical pikachu is better or MAYBE ignorant.
My best advice would be dont relay too much on ratings, they are good but can also be bad too. Learn about the stats and natures yourself and be your own judge.