From what I understand, Farfetch'd is designed to be worse than Fearow specifically. Because its inspiration refers to both a stroke of good luck and a gullible fool, it shows up as an in-game trade for a very common mon... but is worse than what you would get had you just stuck with Spearow. Fearow has all of its stats higher than Farfetch'd (even if that's only by 3 for its special), and gets Drill Peck and Hyper Beam that Farfetch'd doesn't.
Heck you could argue that Fetch'd not getting Hyper Beam itself shows an intent for it to be weaker than other fully-evolved mons.
Late reply, but I guess this is one way to look at it. Still, I don't agree completely. While Farfetch'd might seem outclassed by Fearow, I still think it has a specific niche in R/B. It has access to some things that Fearow are missing. First, and as I mentioned earlier, boosted Exp. From what I remember back from when I played through R/B in the past, this made a pretty big difference as it allowed you to grind a lot easier. And as said, Farfetch'd gets Slash, which Fearow doesn't. Farfetch'd also learns Swords Dance, which Fearow doesn't get either. And Cut, which means it can do some extra side-work as a HM slave, which Fearow can't (apart from Fly).
In comparison, Fearow does get Drill Peck, that's true. And while it can learn a bunch of good Normal-type moves through TM, none of them are optimal. Take Down and Double-Edge cause recoil, Razor Wind requires charging and Rage is broken in an idiotic way. Hyper Beam is great, but it is expensive, has low PP, and if it fails to KO, it requires a turn to recharge afterwards. Fearow learns Swift, which is worse than Slash, but I suppose it should still be decent enough. Other than that, it does not learn Body Slam through TM (though if you ask me, it would have been a waste to teach that move to Fearow), and it only gets Fury Attack through level-up.
If anything, I feel that Fearow is designed to be a worse Dodrio, as Dodrio has higher Attack and Defense at the cost of having slightly lower HP and Special (of which the latter doesn't matter anyway) and equal Speed. Dodrio also learns Tri Attack through level up, which is a great Normal-type attacking move. The big negative for Dodrio is that it is available late, while Fearow is available early. But if you can wait a little, your reward is the best bird! I also think that while Farfetch'd might not be the best Kanto bird, it defintely has a specific niche with Slash, Swords Dance and Cut. That said, it doesn't learn Slash until level 39 in Gen 1, which is fairly late. Still, I remember it being pretty good when I used it on my in-game teams in R/B.
I will also admit that I might be a bit biased here as I like Dodrio and Farfetch'd but I am not overly fond of Fearow. Or Pidgeot, for that matter. Pidgeotto is cool though. A minor annoyance of mine is that I dislike how Pidgeotto loses all of its coolness when it evolves into Pidgeot. I feel that Mega Pidgeot does nothing to improve upon it either, in terms of design at least.
Guess I should post some actual, more serious annoyances of my own while I am here. There are a very large number of things that I dislike about HG/SS, so I might as well post some of them here just to get them out of my head. In the past, I had planned to make a long post featuring all of these things, but I have decided to not do so because it feels pointless and I dislike creating too much negativity. Instead, here are two small things that annoy me about HG/SS.
First of all, I find it really annoying how you can't Fly between Johto and Kanto in HG/SS. When going from one region to the other, you have to do a middle landing at either Victory Road or the Pokémon League (alternatively Mt. Silver or New Bark Town when you are going from Johto to Kanto) instead of being able to fly all the way to where you want in the other region in just one go. I can understand why this wasn't possible in G/S/C, these games had technical limitations and the map was split in two. But in HG/SS? I just can't find any reasonable explanation. There shouldn't be any technical limits for these games, and unlike in the originals, they have both regions on the same map. As for some in-universe explanation, such as "Pokémon can't fly too long distances at once without getting too tired" or something, I don't think it makes sense either. You can fly from the Safari Zone to New Bark Town without issues, but flying from New Bark Town to Pallet is too much? I'm not buying that. The only other alternative I can think of is that they wanted to encourage players to take the train (or boat) instead when traveling between the regions. But those alternatives are a lot less convenient and take longer time compared to flying, so it doesn't really work very well. So, unless there is some technical limitation here that I am unaware of, this feels like bad gameplay done on purpose. Just like in many other instances in HG/SS, sadly.
As for the second thing... I am currently playing HeartGold, farming Yellow Apricorns so I can get Moon Balls for a future capture project. I decided to check if they sell them at the Pokéathlon, since they do so on some days. And today is Friday, so they are being sold there! I had no Pokéathlon points on the game, so I participated in two Pokéathlon courses to get some points... speaking of which, I am not super fond of the Pokéathlon. Some events are quite okay, almost fun even, while others are complete and utter garbage. I have mixed views on it on the whole, it is not the worst minigame in the series but far from the best, I think it is highly overrated though. But that's not what I wanted to talk about. After I had obtained some points, I went to buy some Yellow Apricorns... except that it seems like it is only possible to buy one of each specific item at the Pokéathlon every day. So that's annoying. After getting one Yellow Apricorn today, I can't get another one until Tuesday, which is when they will sell me another one... I have expected this to take some time, but honestly, I think I'll just stick to farming Apricorns from trees. While it is also a bit annoying for multiple reasons, I defintely prefer it over the idiotic way they are being handled at the Pokéathlon.