I do not believe that any sentence works as a 'deterrent' simply because I do not believe that anyone commits a criminal act of any kind with the thought of consequences, legal or otherwise, in their mind at the time.
But, if sentences are offered as a 'deterrent', then they need to be commensurate with the level of damage done by the criminal - and this is clearly not the case here.
In a case like this, the fact that the accused showed remorse and pleaded guilty are taken into account when sentencing.
But that does not mean that the accused believes themselves guilty, or that they are remorseful - rather more that their defence counsel ash advised them of these tactics as a matter of course in order to use the system.
If the laws are framed by the people, and reflect our society's attitudes towards crime and criminals, then it is time that the sentencing guidelines for this type of crime are overhauled as a matter of urgency.
This level of punishment is an insult to the families of the victims, and their level of 'deterrent' is without any real meaning whatsoever.