hmm automatic-inbuilt in rating for pokemons...
next have the game show you the best place to hunt certain pokes...
its not possible to get all 31 ivs and best nature at the same time.
And even if the dev decided to implement it..the rating will vary and wont match exactly with the players thought.
not sounding to be rude but If players want to know which pokemon is good or bad then they themselves will have to put effort and research about it.
And to much work for devs its like you give someone the hand and they take the arm.