I think that is only part of what they were saying, I think you are missing their point a little bit. I think they were also saying that it puts the CPU at a disadvantage because as they progress their players in the attributes scheme, the human keeps putting them down. The CPU doesn't "know" that you are intentionally lowering those attributes, so it keeps training them and it is useless because the human just keeps putting them back. I don't think the post was about "not fitting the archetype" at all.
It is less about the running backs staying in their scheme than it is about the CPU wasting upgrading attribute upgrades and training XP because the human player will keep artificially deflating those ratings.