"That's probably the step other sides haven't made yet. South Africa may have played the better game, but got beat by a point. So I don't think the gap is too big. Which is great, it's what rugby needs. It doesn't need one team that's unbeatable, because that's boring."
Despite the All Blacks' unrivalled success in the Rugby Championship, Henry believes his former team will be faced with some staunch opposition as they attempt to claim their third consecutive world title at the 2019 World Cup in Japan.
"The World Cup is two years away and I was pleased to see Australia and South Africa improve a little in this Rugby Championship series because I think rugby needs competition," Henry said.
"It was pleasing because Australia and South Africa have fallen away pretty poorly in recent times. Against those two teams in the last two games against the All Blacks, they've been great contests with superb rugby. That's really pleasing.
"It's obvious the culture of the South Africa and Australian teams are becoming stronger and I think that's good for rugby.
"There's no point having one team much better than everybody else because that doesn't create interest. When you're not coaching you want a competition and when you're coaching, you don't.
"So going into the next World Cup, for sure I think teams can stop them. England are on a bit of a roll and have lost just one game since Eddie [Jones] took charge.
"The All Blacks will be favourites I would imagine in 2019, along with England, Ireland, Australia, South Africa, the usual enemies will all be out there."