THe trouble with police involvement with DV is that there is only so much they can do, even if they take it as seriously as it deserves.
They can arrest if they have reasonable grounds to suspect an offence has been committed, and they are now duty bound to report the incident, check with SS about the welfare of the DC, etc. They can also refer to the DV unit if the case warrants it, but that like many things in the public centre is resource dependent and so tends to be done by priority rather than as standard.
I've lost count of the amount of cases I've seen properly dealt with by police go precisely nowhere because either the CPS decide there isn't enough evidence to proceed, or a magistrate decides that a few hours community service or a compensation payment is suitable recompense. The trouble is - and this isn't an excuse - some police officers get very jaded by this, knowing it won't go anywhere and knowing that quite often the victim will be unco-operative as well, and so they fail to do as thorough a job as they could, doing instead the bare minimum to fulfil their job requirements.
Now that's not acceptable. But one of the best ways to improve things is to get the courts to take DV more seriously and to maybe change the law to look at different ways of gathering evidence for the sort of offence, which unlike other assaults usually takes place behind closed doors with no witnesses.
Another problem is that the police cannot wave a magic wand and prevent an abuser being abusive. They cannot stay permanently resident with a victim either in a relationship or having ended one, in order to deal with an abuser at every single time they are being abusive. All they can do is respond to a 999 call made by the victim once something has already happened or is imminently about to (and often has by the time they arrive).
Futhermore, the difference between civil law and criminal law means that many forms of abuse are best dealt with using civil law to prevent them (albeit with a power of arrest attached), especially as some forms of abuse aren't criminal. Many people don't understand this difference.
To complicate things even more, most victims put up with a lot of abuse before they ever call the police (about 35 incidents on average) and very often take their abuser back once the dust has settled. It needs to be understood by victims that the police cannot stop that person being abusive and remaining in the relationship. Remaining in the relationship carries the certainty risk of further abuse that the police can only turn up to afterwards. Further education in PSHE style classes about healthy and abusive relationships and how abusers rarely change might help with this.
But what we really need is a cultural shift, where abusers are ostracised by wider society and there are serious consequences even for 'milder' forms of abuse. At the moment, abusers suffer little in the way of consequences unless their abuse takes the form of serious physical injury to their partners (and I'm talking more than a black eye), which is something the police have no control over. They are not judge, jury and executioner, they are simply the first point of contact in the criminal justice system. As long as an abuser can retain their job, friends and family, they will continue to abuse. And the victim will continue to be blamed because it's more comfortable for wider society to believe that.
The police are quite rightly being held more accountable for abuse cases. As they should be. There is still room for significant improvement and some old dinosaurs and outdated attitudes that should be put firmly in the past. But the police are not gods who can make everything ok and unless we have massive legislative change, that isn't going to change anytime soon.