He has had to learn to walk, talk and eat again but only has the cognitive abilities of a child and needs help with the most basic tasks.
Mr Bryden's mother, Vicki, said politicians needed to see what her son had suffered to realise more must be done to curb the binge-drinking culture.
"I wouldn't wish this hell on my worst enemy," Mrs Bryden said. "I really don't have the answer ... but something somewhere needs to change."
Tuau had earlier pleaded guilty to wounding with intent to cause grievous bodily harm over the attack, described by Justice Miller as "frenzied and brutal".
The pair were strangers when Mr Bryden, who his family says was not a big drinker, asked a woman arguing with Tuau outside a bar if she needed help.
When Tuau said they did not, Mr Bryden punched him in the face, knocking him to the ground, and walked away.
Tuau and two others chased Mr Bryden before Tuau punched him to the ground and repeatedly kicked and stomped on his head.
Mr Bryden spent days on life support before Tuau handed himself in to police.
Mrs Bryden said her life turned upside down when she heard about the attack. She would never forget the fear that her son would be dead after completing the hour-long drive to Wellington Hospital from their home on the Kapiti Coast.
"What greeted me was devastating. I could not recognise my own son," she said.
"Robert stepped in to what he thought was a woman being harassed and he did what he thought was right. Yeah, he hit him first and he walked away and that was that, and they hunted him down.
"Every day I hope that this will be the day my son recognises me and says 'hi mum'," Mrs Bryden said.
Defence lawyer Elizabeth Hall said Tuau, who now plays for club side Te Aroha Eels, was of good character and had completed community work.
He accepted he had a drinking problem and his four breaches of bail since being charged were evidence of his immaturity.
But Justice Miller said Tuau's attack stopped only when a woman intervened.
"You very nearly did kill him," he said.
"In my opinion your crime is among the most brutal, the most harmful, the most serious of its type."