Okay...I don't think it's some kind of conspiracy. If you co wash, you have to be cautious of what's in your conditioner because build up can happen. Imagine someone heard of co-washing in passing and tried to co-wash with a conditioner full of cones and then used RO and LI full of cones. They probably wouldn't have a very pleasant experience. Obviously since you are using shampoo, you don't have to be hyper sensitive to build up. You could even suggest that a little build up might be a buffer between surfactants and your hair.
It's all common sense. You don't follow anything word for word without taking in context and intent.