The problem is it makes a lousy metaphor. In Taijiquan our weight does not shift back and forth like a lever. Perhaps like a tube of toothpaste, or a bag of something fluid, but not like a lever. Sure we can manipulate the fulcrum of two forces to throw someone, for that it could be an apt metaphor, but the metaphor it isn't used like that.
Louis Swaim translates: "Stand like a balance scale; active, like the wheel of a cart. Sink to one side, then follow. If double weighted, then one will stagnate...." Sounds fishy to me.
We are not talking about a scale as an object, we are talking about a scale as a function. The function of a scale is to represent things exactly as they are, with no mediation. Scales are honest. Scales are always appropriate.
If you put 5 pounds on a scale, it shows you 5 pounds, not 4.9, not 5.1. It adds nothing and it takes nothing away. When I practice Taijiquan, that is what I'm trying to do. If you give me 5 pounds, I simultaneously give you 5 pounds back. If you push me I don't resist, but I don't run away either. I respond exactly to what you give me, nothing gets in the way.