As the OP I asked the question "Is there something wrong with sentencing guidelines or with judges or both?". It's not any specific crime, criminal, offences, or offender, frequency or difficulty of reporting or of prosecution. Feel free to start a different thread or threads about the other matters. And it certainly isn't about crimes/sentences in other jurisdictions.
We were discussing ideas related to the sexual assault case you posted about earlier in the thread. And it's Letting Off Steam.
Yes, there is probably something wrong with both sentencing guidelines and judges. But there has been gradual, steady improvement in transparency and consistency of sentencing.
Sentencing is decided based on multiple factors to varying degrees, including: precedent, Irish statutes, the Constitution, the ECHR, etc. And yes even by crimes/sentences in other jurisdictions. And as we were discussing above, judges are human beings influenced by their personal experiences and social norms, both negative and positive.
On conviction there is a headline sentence of let's say 10 years. The judge takes off 1 year because the criminal pleaded guilty right away, sparing the victim a long process where they would have had to give evidence, and sparing the state the expense of a long trial. The criminal has no record, so the court gives another 1 year off (de facto penalty for repeat offenders). The criminal has a serious drug addiction so they are given 6 months off (lower culpability?). Since committing the crime they have gone through rehab and are now back in education, another 6 month off (rewarding people who make a positive change, de facto penalty against people who do not). And so on.
These are done so that people are rewarded for doing things that benefit the victims, the courts, the state, or society in general. Encourages early guilt pleas, promotes rehabilitation, takes into account the circumstances of the criminal/crime, etc.
I often wondered why people were not given a base sentence and then penalties applied for not co-operating, but I was told it would be against core principles of our legal system. It could be seen as a punishment for people who insist on their right to a trial, presumption of innocence, right to silence. It seems like sophistry but I suppose in general we know it is more effective to encourage positive action than to penalise negative ones.
Every crime is different so it seems sensible that the court would have leeway to reflect that. It's inevitable that there will be disagreement, no matter what approach is taken.