"In terms of influence, Barrett has a lot more on a game. And his ability to counter attack from the back is unbelievable.
"Cully had a natural instinct to beat a man and it was his ability to step and stay at the same pace which really got defenders going. But shifting Cully (positions) didn't work. Barrett can take the reins and be the main man.
"You'd give Cully the ball early, stay inside in case he passed, but usually it was never the case because he finished every chance he got. I used to call him crowbar, because he never passed the ball."
Cullen says the British and Irish Lions will face a massive problem trying to contain Barrett.
"How do you stop him? I'm sure the Blues talked about shutting him down, don't give him space. And look what happened?," Cullen said.
"He slips back into that fullback role and lets rip. At the moment he's in great form and hopefully that continues through to this Lions tour.
"There is no substitute for speed and he has plenty of that. You see him running across field, it doesn't look like he's running that fast, but he's just evading people, they think they've got him and he's gone.
"In that try off a scrum (against the Blues), there was vision, timing, decision making. The ball was in the left hand, then in the right, two hands, a dummy, then he found Laumape.
"He's calm under pressure, and obviously has a pretty clear head. I say this in a good way - there's not a lot going on (in over-thinking). One of the good things (at the Hurricanes) is that he doesn't have to worry about the goalkicking now. His brother is good at that. He can just play his game."
Murray Mexted, the former All Black forward and Wellington icon, said "when Barrett is around, things happen in every game".
"We know he has the skills but aside from that, he has the temperament, work rate, decision making, makes instant decision on the ball all the time. You might say he gets a lucky bounce all the time, but if it is all the time it's not luck," said Mexted, who runs a rugby academy.
"He picks up anything loose, gathers it in, it's his lunch, he's feeding off the tiniest mistakes. Sometimes they are not even mistakes - he anticipates and creates opportunities for himself.
"And when a No. 10 attacks the line like that, it creates so many opportunities for backs outside."