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That's the verdict from commentator Jeff Wilson, one of New Zealand's finest outside backs, despite McKenzie's blistering displays in Buenos Aires and Cape Town.
Springbok great Joel Stransky also entered the debate, plumping for Smith although he suggested it was a close call.
Wilson was unequivocal on the matter, telling the Radio Sport Breakfast: "There's no doubt Damian McKenzie is one exciting player to watch.
"But gosh we've got short memories. He (Smith) is the best fullback in world rugby on both sides of the ball.
"There is no doubt there are fantastic things this young kid McKenzie can do.
"He can create something out of nothing, has great acceleration, has all those wonderful attacking things.
"But you should never get blinded by one aspect of the game. Only a couple of test matches ago in New Plymouth, he was really challenged under the high ball by Argentina.
"There are still a number of things in his game he will need to work on.
"Look, he's a brilliant and talented footballer with great potential but for me, Ben Smith is a proven man.
"The great versatility he has gives us the luxury of having this discussion as he can slot onto the right win if we feel that is the right place for him.
"And we shouldn't forget how good Jordie Barrett is."
When RS Breakfast host Nathan Rarere wondered tongue-in-cheek if Smith might consider rushing back from a sabbatical to cement his spot, Wilson said: "No, not at all. He's resting up, getting ready for a big Highlanders season.
"He understands it is an opportunity to freshen up.
"For the All Black selectors this is a perfect opportunity to develop another player, and we know how good they are in the All Blacks environment.
"McKenzie is getting better and better, it's exciting. It's time in the saddle, playing test match footy, getting more and more experience.
"It's his responsibility now to learn from every outing."
Stransky said the choice was "a tough one", but with Smith's more physical game vital in the World Cup
"Ben Smith is an unbelievable player who brings huge experience and commitment. He has a different type of game to Damian McKenzie," Stransky said.
"There is no doubt there is a place for Damian McKenzie. He showed on the weekend tremendous acceleration, unbelievable pace. You give him a little bit of space and he's courageous in the way he carries the ball forward.
"Whew...but as good as he was on the weekend, I'd be inclined to say come World Cup time in a match where every second and opportunity counts, I might be opting now for Ben Smith."
See what Radio Sport listeners reckon on the Smith v McKenzie debate: