I knew someone would give this argument - to which I agree on some ways, because it is totaly true from a pvp point of view - but I continue to think that there must be some pokemons with more value than others (just because more people want them or because they are more used). The difference has to be made between the intrinsic value and the exchange value, as people like Smith pointed it out (the latest one being the one which interersts me).
If i take your exemple of ratata for instance, I'm not sure il would be worth to catch all ratata you find on your way - because they are not rare and a lot of person do not use them - and they do not worth the price of a hyper ball.
But if you find an abra on your way, I think that is is worth to catch it anyway (because it is easy for him to have value and is more used by pokemon trainers).
I think that putting all pokemon on the same scale is not realistic considering the offer and supply that exist on a market.
Thanks for your answer anyway.