In relation to trading, I don't really get why trade-backing Pokemon caught in your own game is singled out as the sort of acceptable "bring in outside forces" option. You could probably just as easily get someone to trade you a Houndour for example, which only requires
one trade, not two, and train that Houndour with boosted Exp into an earlier evolving Houndoom which may be able to rampage over the game (I haven't put particular thought into whether or not it can, but early-game Houndour isn't on the list yet trade-evolved Pokemon are).
Not to mention the possibility of trading to a friend, having them buff up your Pokemon with evolutionary stones, TMs, vitamins, Rare Candies, and trading back. Or just having them send you a Pokemon with one helpful item attached (a stone or TM). Is this really that much ahead of a tradeback in terms of convenience/difficulty? Especially with stone-evolved Pokemon. Vaporeon can rampage through the game with just Surf and even just Aurora Beam and Bite backing it up. Once you are bringing an outside factor into it, is it really that much more of a stretch to expect a friend to stone evolve your Eevee? I don't really think it is.
Or look at it this way. Where is the bigger gap in the following, when it comes to how it should be penalized:
1. No outside involvement (ex: catching an Abra and playing through with Kadabra)
2a. Trade and trade back (ex: catching an Abra, evolving to Kadabra and then trade-evolving)
2b. Trade an outsider Pokemon to your team which took little effort to catch (ex: Houndour, Larvitar, or even a Graveler)
3. Use outside help to make a stone evo (ex: having your friend trade you a Pidgey with a Water Stone attached, and then taking that Water Stone and giving it to Eevee)
In my very subjective opinion, the big gap is between 1 and everything else. 2a, 2b, and 3 should all be heavily punished in tiers relative to 1, and not so much relative to each other. Before you say "well they have to get really far in the game to do that which takes a lot of effort", how about simply receiving a Totodile or Cyndaquil?
So basically, get Alakazam the hell out of any high tier