Forgive me if this is stupid, but why must te NFE follow it's evolution as opposed to being treated as a seperate Pokemon? To illustrate me point, we have powerful NFEs like Scyther and Sneasel and puny ones like Combee. Whether you put them with their evo or not, one will not make sense. Scyther is too tough for lower teirs but Magiarp in OU is absurd.
Who is suggesting that Magikarp should be OU? It's a pure water type in comparison Gyarados; it also has the ability "Swift Swim". I don't know how anyone can argue regarding this Magikarp issue because it is different from Gyarados (Not OU-lite).
Scyther is much different than Scizor when compared to Sneasal and Weavile <.< the latter are basically the same pokemon, whist Scizor and Scyther have a different typing and stat distribution, each having pro's and con's over the other. Ex. Scyther's speed compared to Scizor's Defence.
A possible solution would be to assign a tier to every Pokemon, but this would of course be time quite consuming.
An alternative would be to take the final stage as a reference point and to rank the NFE based of this. For example, a Pokemon that mirrors its evolved form, like Sneasel does then it would fall under the same tier, but an NFE which is obviously as inferiour as Metapod or Kricketot would be moved to a lower tier. An NFE that functions differently to its evolved form, like Scyther, should be treated with a fresh analysis.
Or am I totally off?
Your generally right. If a NFE is different enough from it's evolution (Scyther,Vigoroth,Pikachu,Metapod even due to typing and trait) then it should be treated different as a standalone pokemon.