She said the 27-year-old man who was struck in the face received a wound running almost the entire length of the right side of his face and he had lost feeling in part of his nose.
"Lucky there wasn't more serious injury, like the loss of an eye," Crown prosecutor Kirsten Lummis said.
"Or death," said the judge.
The Crown also pointed to Neilson's premeditation and the fact he had chosen one of the busiest malls in the country to commit the crimes.
But the man's lawyer Emma Priest said the "foolish, youthful" decision was made spontaneously while drunk, in a bid to get more money for booze.
Though she passed on Neilson's apologies to the victim, a probation report painted the defendant as "nonchalant", according Judge Cunningham.
The probation officer said he had little remorse or insight into his offending and appeared to lack the motivation to address his alcohol problems.
Ms Priest said the Wanganui-raised Neilson had dropped out of school at 15 and soon turned to a life of crime but was now motivated to take advantage of educational opportunities behind bars.
The judge highlighted almost 50 previous convictions, which portrayed an "unstructured, almost criminal lifestyle" over the past seven years.
During that period, Neilson had been convicted of various dishonesty offences, as well as threatening to kill and assault with a stabbing instrument.
And only five days before the Sylvia-Park incident, he was stopped by police in Huntly in a stolen car, resulting in a charge of unlawfully taking a vehicle along with those of theft and aggravated wounding.
The summary of facts said he had refused to comment to police but was too intoxicated to do so anyway, Judge Cunningham said.
"You don't seem to appreciate how serious your alcohol problem is. It seems to me like once you start, you can't stop," she said."
"A decision never to drink again would be a good one, Mr Neilson."
The judge had considered imposing a minimum period of imprisonment but decided against it because of Neilson's youth.
