Some cases it's like you say, but in a lot of cases the judge has a lot of latitude and doesn't sentence the SO to much time at all.
Remember the judge in Vermont who gave a man a few months for sexually assaulting a little girl? I think she was five years old.
Then if the SO gets “treated” in some program they can get early release with little to no restrictions.
This type of offender is the worst type, because they are not treatable and it's a guarantee they'll repeat their crime.
I remember that case. That was a crazy judge who wouldn't follow the prosecutor's recommendations. That's not the norm, at all. Actually super liberal trial level judges aren't the norm. They just make for good news stories that get people worked up and help sell a lot of advertising. In real life trial court level judges tend to be prosecutors in black robes who want to nail everyone. Of course in most states they are elected and the last thing they want to be known as is liberal, soft on crime. Usually if it's up to the judge the judge will nail people really hard. They want as many cases resolved by plea as possible. They're hard on defendants so they'll look tough in the news and to other defendants in court and their attorneys. They make examples out of people if they have to do the sentencing so that people will know that the best thing to do in their court is to shut up and plead. The more people plead the easier their jobs are. If too many try their cases, judges’ jobs become impossible.
Only something like 2.5% of all felony cases ever make it to jury trial. Almost all the rest are resolved by plea bargain and that's just the way the judges want (and need) it to stay. So, they strongly “encourage” prosecutors and defense attorneys to work the cases out and they rarely ever refuse to go along with whatever deal the attorneys work out. This isn't what happens “some” of the time. This is what happens almost all of the time in state courts in most parts of the country. I know a little about this. I've been practicing law a lot of years in a lot of different courts. I've prosecuted and defended people, handled thousands of criminal cases, including quite a few sex offender cases.