This was a civil, not a criminal case, and the judge had to decide whether he believed Mitchell, who had no corroboration to his account of what happened, or 5 police officers who each backed up each others account
So, the same thing would apply to the police officers who were disciplined then, and indeed the 3 Fed Reps. The Balance of probability is the standard used for them on Discipline hearings. So by your reckoning, no police officer found guilty at one of those actually did what he was accused of?
Anyway, thats neither here nor there. Had you looked for the evidence that was presented, it was all there. Mitchell's behavior over many years was of a similar standard, he admitted he was bad tempered, his story was very inconstant. The Judge also said he was "Impressed" with the Police officers evidence. He didn't say the same of Mitchell. In any court hearing part of the reason why the witness is always seen by the magistrate/Judge/Jury when giving evidence is so that they can see the way it is delivered and use that as part of their assessment as to the truth or otherwise.
He wasn't taking on an organisation, well, the Sun, he was taken on by a Police Officer, who obviously didn't want his reputation tarnished, and lets face it, why should he put up with it? The fault lays entirely with Mitchell.
The Judges words were that he was satisfied to "At least on the balance of probability".
What Mitchell has now learned to his enormous cost is that if you're going to sue a government department or a large organisation with unlimited resources for libel, you need to be very sure that you have the evidence first, and that the evidence needs to be documentary (video, audio or written) because you can be sure that the other side will always find whatever verbal evidence there may be from enough witnesses to cast doubt on any verbal evidence that you have. It's a numbers game.
No, what Mitchell has learned is not to be rude to the Constables in future, and if you are, not to lie about it, or accuse the Police officers, falsely of lying.