Yes, the Huntley case led to the Bichard inquiry which in turn led to the founding of the Independent Safeguarding Authority, which was subsequently merged with the CRB to form the DBS. The inquiry also led to various procedures being tightened.
In safeguarding training, we always tell trainees that DBS checks on their own are not enough. They will only tell you about convictions or, rarely, cases where the police have relevant non-conviction information.
The judge uses the small number of trans staff and the vetting requirements to argue that allowing trans-identifying men into the women's toilets was not likely to place women at a greater risk of violence of sexual assault in the toilets than men. However, from a safeguarding perspective, I would say that vetting may help to reduce the risk, but it does not eliminate it. We know that, on average, child sex offenders commit around 100 offences before they are caught. I don't know of any equivalent figure for violence or sexual assault but, given that the vast majority of sexual abuse incidents are never reported to the police, it is also likely to be high. It may be that none of the trans-identifying employees at Leonardo are a threat to women, but it is clearly wrong to say that the small number of such employees and the fact they are vetted means there is no risk or that it reduces the risk to the same level as that faced by men.