I think we're seeing that, time and again, tacticians and technical coaches are more successful than coaches who lean heavily into motivational skills. Thorn and Cheika are culture coaches, who care more about intent than form. Gibson and Wessels seem to care mostly about results, but the former doesn't really know how to get them, and the latter can't unify the cores of two teams so his tactical skills are generally useless.
I don't know how much of a tactician McKellar is, but he clearly has a technical legacy. I wonder how much squad management is done directly and how much is managed by assistants or influential players. But when you have guys like Hewat and Fisher there, you know the tactical side is probably covered and that you will have options; you just need to pick the right one.