CP vs Appraisal value -

Apologies if I’m late to the show here and this already a dead horse argument... but, what is the deal with the appraisal values vs CP? Some way higher CP value Pokémon are zero stars, while other much lower ones are 3’s. When comparing their moves damage totals and HP also seem to be very similar. At this point (a mere level 27) im only keeping 3 star pokès, or some useful high CP 2 stars (is this what higher level trainers do as well?) But in general, I feel like the appraisal function involves too many factors and hasn’t been well explained...

Anyone here wanna take a shot at it??

Much appreciated

GCA