Mika ignored his passengers' requests to stop and allow them to leave before he struck a road barrier, causing the vehicle to roll on its roof.
Ethan was thrown for the vehicle and killed while Mika ran away without checking whether anyone was injured.
Mika's lawyer, James Rapley, submitted to the Court of Appeal that his client should be entitled to a 10 per cent discount on his sentence to reflect his Maori heritage and thus social disadvantage.
He submitted that the sentencing judge should have taken into account the "unique systematic or background factors leading to the appearance of a Maori offender in court".
Mr Rapley emphasised the disproportionate representation of Maori in New Zealand's prison population.
The court accepted that disadvantages suffered by many Maori frequently contributed to offending, "but it does not logistically follow that a person is more likely to be at a disadvantage and to offend simply by virtue of his or her Maori heritage".
"To some, such a proposition may appear offensive," the court's decision said.
The appeal was dismissed.