It's more the inconsistency of results than anything else. 2013 was rock bottom for the Highlanders, although he obviously learned from it and made big changes. During his Lion's tenure, Wellington lost 2 finals & a Semi-Final with an exceptionally strong roster.
With Japan, he's shown he can do well at a home World Cup with 9 months of preparation with the players in camp (note - that no other country had this advantage due to Japan's Top League season finishing in January 2019 that year), but he's had some pretty atrocious results outside them - getting annihilated by some T1 teams, almost losing to Portugal, etc. He really seems to target specific games rather than being consistent throughout.
As Gatland said, there's "only one" standout coach in NZ rugby & it's Razor. Rugby Australia ought to throw the money at him.
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