You’re comparing apples and oranges though
He got sacked for committing gross misconduct, in uniform/at work too. Most people would for slapping the arse of a 17 year old. That’s separate from the criminal recourse
He got convicted because presumably there were witnesses and evidence - and because there’s a clear pattern of him harassing her over months and making multiple sexual comments. It wasn’t an isolated incident so easier to paint bad character. Likewise, this is why he was placed on the register - he was actively targeting her and becoming more intense. It was effectively a slam dunk.
Rape convictions have difficult succeeding due to the high bar of evidence needed and the fact that there usually aren’t witnesses so it’s one person’s word against another