I heard that farfetch’d was put in the game to teach players a ‘lesson’ about trading a spearow that could evolve into a fearow for something that will only have limited usefulness (because fearow is so godly, right?), just like magikarp is there to be a lesson. You know what I did with magikarp? I put it in the daycare until the end of the game. It was at level 31 by that time and evolved into gyarados with no effort. Isn’t that what everyone did? Their lesson was lost.
Everyone? I beg to differ. Personally I’ve never done anything of the kind. And I think the point is there all the same – you evolved your Magikarp with no effort, but waited until the end of the game for it to reach a high enough level on its own, so you certainly had to exercise patience. Even if you catch a Magikarp at level 19 and use a Rare Candy to evolve it immediately, Magikarp still expresses one of Pokémon’s central themes, that something small and weak can grow into something great and powerful with the right kind of care. I don’t think we have to interpret Magikarp in such a narrow way. The lesson is “lost” if you choose to ignore it, but that’s always been the case for everything.
As for Farfetch’d… well, yes and no. It makes sense with Farfetch’d’s… wait, that doesn’t look right. Farfetch’ds? Farfetchd’s? Farfetch’s’d?
…it makes sense with the design of Farfetch’d, in that the “duck with a leek” concept refers to a Japanese idiom meaning either an unexpected blessing or, basically, a sucker (depending on your lifestyle, these may both be applicable to the same person). In this case, either Farfetch’d is the blessing – a rare Pokémon otherwise unobtainable – or you are the sucker – making a trade for a Pokémon that… well… sucks. Ultimately if you want to finish the Pokédex you need a Farfetch’d one way or another, so from that perspective it’s a good deal, but maybe on some level you still feel like you’re being ripped off (for bonus points, compare the way Farfetch’d is portrayed in the anime – one of a duo of con artists whose default scheme involves swapping something valuable for something useless). The result is that we have a Pokémon who is, possibly, just supposed to be bad, to the extent that if Farfetch’d ever evolved and actually became useful it would ruin the joke (and I think that’s what it is – a joke, rather than a ham-fisted lesson – because, hell, Spearow’s not that great anyway). It’s an unfortunate conflict with the previous theme, the idea that even the weakest Pokémon like Magikarp will become powerful with care and diligence… but not one that Game Freak seem terribly concerned about.