I'm not sure it's completely true - from a legal standpoint - to say that no real sentence at all was handed down. (Please take this in the spirit of looking at this from a legal POV. My own personal opinion is that the sentences are a disgrace.)
If you look at the sentencing guidelines, a YRO with ISS - which is what NR handed down - is the second harshest sentence which can be passed. In order to hand down a custodial sentence, not only does the crime have to be particularly severe (as I agree this was) but the judge also has to justify why a YRO with ISS is not appropriate. In other words, a custodial sentence would only be passed where there is literally no other option:
"If a custodial sentence is imposed, the court must state its reasons for being satisfied that the offence is so serious that no other sanction would be appropriate and, in particular, why a YRO with ISS or fostering could not be justified.
Where a custodial sentence is unavoidable the length of custody imposed must be the shortest commensurate with the seriousness of the offence."
https://sentencingcouncil.org.uk/guidelines/sexual-offences-sentencing-children-and-young-people/
It's not right and I fully understand the outrage this case has generated. But in my opinion the issue is with the law and sentencing guidelines and not with the judge.