I've read the judgement from end to end, twice.
It's pretty clear that naive "independent" psychologists, at least one of them in the pay of Worboys, were willing to be taken in by an accomplished liar. Experienced prison psychologists said he should not be released, but were over-ridden on the basis of a 40 minute questioning of Worboys at which inadequate notes were taken. The issue of further offending was not investigated, and the court quite rightly expresses its scepticism at the contention that the CPS by magic managed to charge Worboys with exactly and precisely only the offences of which he was actually guilty.
Those who follow the Parole Board's enthusiastic support of freeing rapists because they're probably nice people really will be horribly reminded of the case of Anthony Rice, who was freed on the basis of flawed assessments by do-gooders and went on to commit a murder. The whole case, which shows that the claims of the Parole Board to be sharp and incisive are rather self-serving, can be read about here in the report by HM Inspectorate of Probation, as it then was.
Whatever the mistakes make by the police in not bringing more cases to court, surely the principle of innocent til proven guilty should still apply,
In the case of Parole hearings, no, that should not apply. It is the task of someone applying for parole to show that they do not present a risk to the public, not the task of the Parole Board to show that they do. Worboys was given an indeterminate sentence. At the parole hearing, the presumption should be that he not be released, unless he can show that he does not present a risk. A reading of the judgement shows that was quite clearly not made out, even if you discount the uncharged offences (ie, looked at solely on the basis of what he was convicted of, his sudden switch from claiming innocence to "accepting" his guilt is not convincing). It's precisely what happened in the Rice case - an accelerating race towards release, based on the most optimistic reading of the evidence, on the assumption that ultimately release is inevitable and the question is "when?" rather than "whether?"
The parole board seems to have done its job
The court, given all the evidence, disagrees. See paragraph 159 onwards.