Not absolutely true but the basic concept that induction is reduced is correct but harmonics ensure it still exists.I'm confident that there was a discussion about this several years ago where the concept of induction effects were debunked because the current in the live wire EXACTLY CANCELS the current in the neutral wire which is flowing in the opposite direction.
Adding an iron core would have an effect if induction was present BUT who would reduce their payload AND give themselves extra work in lifting the cable by doing such a thing?
Gordon
I was joking though. As you say, why would anyone want to carry such a lump of iron.