Sentencing guidelines say the following. As well as reductions in sentence for showing genuine remorse the following reductions for pleading guilty would normally be expected.
First reasonable opportunity to plead guilty 1/3 reduction in sentence.
After a trial date is set 1/4 reduction in sentence.
At the door of the court of the court after the trial has begun 1/10 reduction in sentence.
As shown here, if he'd shown pleaded guilty as soon as he was accused, he might only be looking at years. Out in 24 months and he'd have done 12 months already. Had he not only pleaded guilty but had expressed genuine remorse (been to therapy to address his underlying sex issues, taken steps to sort his life out etc) he might have been looking at 2 and 1/2 years and could have been out this summer.
Arrogant Johnson deserves all he gets I'm afraid.