The buddy system is kinda unbalanced. For example:

Magikarp gets 1 candy every 1km walked. Now given the fact that the game is dubious in it's distance tracking at times (I can walk fast enough to trip the "you're moving too fast" so god knows what it would do if I was to actually take my phone out on a run), this means you would have to walk at least 400km to get enough for a Gyarados. Ok, so Gyarados is top tier but 400km... lets put that in real terms: It's approximately 465km from London to Dublin with tracking problems and the Irish Sea in between, you'd probably not only have to walk that entire distance but still capture a load of Magikarp.

Starters are it seems 3km per candy. If you want a Charizard for example, you need approximately 125 candy (that's a whopping 375km!) to evolve from Charmander to Charizard. Then you need to walk in enough candy to level it up. This if you're near max CP is not so bad. Lets face it, walking 9km for 3 candy to do an upgrade isn't the worst but if your Charmander isn't maxed out, you're screwed.

Personally, I think that the buddy system should be the distance = 5 candy each time it's walked. This would mean that a Charizard is still nearly 30km to walk it in if you can't find a nest of them and bum out on the 2km eggs getting a Charmander. A Gyarados is still approximately 80km to walk it in without any captures. That would still be a bloody long walk (almost the same as London to Brighton and I am sure any person who has walked on a 100km challenge would tell you it's not exactly easy) but much more do-able than 400km!