Crown prosecutor Sally Carter said the sentencing judge "glossed over" the fact Filipo was the "aggressor" in the assault, and "effectively gave too much emphasis" to the effects a conviction would have on his career.
Carter said the summary of facts the judge used during his sentencing made it "very clear" the victims did not want to fight.
Filipo's assertion he was punched first was "at odds" with the agreed summary of facts.
Carter said the judge appeared to have overlooked the fact Filipo had stomped on the head of one victim four times.
"The judge hasn't fully appreciated or articulated the aggravating features to the offence."
The judge "didn't fully recognise the seriousness of the offending", she said.
The judge had adopted a starting point for sentencing of one-and-a-half years, which Carter called "manifestly lenient".
Carter said the Crown believed the starting point for sentencing on the overall offending should be between three and three-and-a-half years in prison.
Carter said the judge allowed a discount for Filipo's remorse, but in his affidavit there had been an element of Filipo not taking responsibility for the assault, and indicating he was not the instigator.
"In the main part, the judge has assessed that the consequences of the conviction mean that Mr Filipo would no longer be able to have a career in rugby and the travel restrictions that would come from a conviction would impact on his career," Carter said.
She said a conviction would not create an "absolute bar" against Filipo playing rugby, including in the UK or France. She said there was no evidence before the court there was a "real and appreciable risk" Filipo would be unable to play overseas.
"In the Crown's submissions the consequences did not outweigh the gravity of the offending," she said.
Carter also said the court should still grant leave to the appeal despite it being filed 13 days late, as the merits of the application were strong.
Defence lawyer Noel Sainsbury said the "breadth and depth of the material provided to the judge about this young man couldn't have been greater".
Sainsbury said offers to pay reparation and attend Restorative Justice, the decision to plead guilty, take responsibility, and exhibit remorse were all factors that could bring down the gravity of the offending.
He said Filipo's case was one of "a young man from a severely disadvantaged background".
He said Filipo was "lucky" that certain people saw his potential, "gave him a chance" and gave him a shot at a career in a professional sport.
Sainsbury said the risk now was to return Filipo "to the dire prospects he had".
"The Judge recognised that. He made a considered, correct and compassionate decision. He was absolutely correct to do so."
Sainsbury said the judge "had the full information" as opposed to what was "cherry-picked" by the media.
If there were issues with the summary of facts, a disputed facts hearing could be held, which would involve questioning the complainants. Sainsbury said Filipo preferred not to do that and instead take responsibility for his serious assault.
Sainsbury did not consider it important the sentencing judge had not referred to the victim's head being stomped on four times. The judge said only that the victim had been stomped on.
Justice Collins said he wondered whether, "give the significance of the stomps to the head", it would have been better for the judge to address it specifically.
Sainsbury read to the court from a letter written by one of Filipo's former teachers.
The writer had taught Filipo on a part time basis for two years, six years ago, and noticed he had "enormous leadership and sporting potential".
"But at that stage he was very hampered by his environment."
Many of Filipo's former classmates and friends now had gang affiliations, the teacher wrote.
"Losi needs to continue to live and learn out of this area. He has the ability to maximise his great potential in a positive environment."
Sainsbury said people who had positive support could still do stupid things.
"When you're 17, well some people do stupid things. He had been warned not to go out with his older brother, but he did, and here we are.
"What's happened is serious and wrong, but that one act of wrong behaviour shouldn't derail all the progress that's been made. The judge was right to see that and saw it. And as I say, the judge had all the information."
A discharge without conviction kept Filipo from returning to an "anti-social environment", Sainsbury said.
"Frankly, society is the better for it."
Sainsbury said Filipo spent time washing cars to raise $1000 for the reparation payment to his victims.
Sainsbury said he had "a concern" in the way the appeal had unfolded, brought on by an "outcry".
"It just creates a real unease . . . how this has been driven rather than by principle but by the views of some individuals who are unhappy with the court process."
Justice Collins has reserved his decision.
The case came to light last month when the victims questioned why Filipo's sporting future should have been a factor at sentencing.
The public and media backlash led to Filipo withdrawing from the Wellington squad, and to the winger and the union mutually agreeing to terminate his contract.
