Without getting into the merits of restorative justice, I actually think the sentencing guidelines are the
result of focusing on the offenders rather than abstract legal principles.
The basic purpose of criminal law is to establish norms for behavior. Punishing any given offender or satisfying any given victim is secondary to establishing a norm so 10 other people won't do the same thing. This is a distinct concept from "deterrence." The idea of deterrence is to force people to include the probability-weighted cost of a jail sentence into their cost-benefit analysis. A jail sentence twice as long means a twice as strong deterrent effect. However, given the practical probabilities of getting caught for many crimes, deterrence doesn't really exist. Say 2 years for stealing a bike times a 0.1% chance of getting caught = deterrent effect of 0.73 days in jail per bike. The punishment isn't deterring anyone. What's keeping people from stealing bikes is the social norm created by making bike stealing illegal and punishing offenders.
This rationale for criminal punishment supports having crimes be punished in proportion to how egregious a violation of the social norm has occurred. That's why punishing someone less for stealing food to feed a hungry child is justifiable. Within a restorative justice theory less punishment is appropriate because a small breach of social norms requires less healing, but that only focuses on the singular event. The additional justification is that a small breach of the social norm requires less punishment in order to maintain the norm for everyone else.
At some point in the 1960's, people (mostly liberals) decided that criminal law should be about rehabilitating the offender. This led to a focus on the offender, rather than the offense. Hence three strikes laws, ridiculous sentencing enhancements or reductions for whether an offender seems contrite at sentencing, etc. Ironically, this thought process also led to an inflation of sentences, because people more easily rationalized increasing maximum sentences when those maximums would only be applied to "bad people."
Of course restorative justice isn't coextensive with the 1960's idea of rehabilitative justice, so I'm not saying it suffers from the same problems.