Ney met sex worker Michaela Dunn at an inner-city apartment on the morning of August 13, 2019 and immediately attacked her with a knife to the face, neck, chest and limbs, before cutting her throat.

He shared gruesome video of the attack's aftermath with a friend on Facebook, bragging about his actions.

Following the murder, he took to the streets of the city centre, shouting made-up terrorist chants and stabbing another woman, Lin Bo, in the shoulder during an attack that she survived.

Ney was apprehended by a group of bystanders, one of whom shoved him to the ground with a chair while another pinned him with a milk crate until police arrived.

During his trial, Ney pleaded guilty to murder and wounding with intent to cause grievous bodily harm over the attacks on Ms Dunn and Ms Bo.

In 2021, he was handed an aggregate sentence of 44 years' jail with a non-parole period of 33 years.

Ney's lawyers argued the killer's time behind bars would be more onerous on him due to his mental illness, which the appeal judges accepted was not directly addressed in the initial sentence.

Justice Robert Beech-Jones said in Wednesday's judgment he accepted expert testimony Ney's "limited intellectual functioning, high levels of anxiety, propensity towards depression, suicidal ideation and poor social skills" would make jail more difficult for him.

The original sentencing judge erred in not disclosing how those factors were considered in deciding Ney's jail term.

The appeal panel ruled a "somewhat reduced" sentence was therefore warranted.

But the judges rejected several other claims by Ney's lawyers, including that the initial sentence failed to properly consider his purported empathy and remorse for the crime.