There have already been rulings that the reasonableness of force does not require exact proportionality (Cross V Kirkby 2000 and Oatridge (1991)). Perhaps this ruling makes that a little more explicit, but it's far from new thinking.
Isn't that what I said?
You said the law hasn't changed. It has, in at least three places. In statute. I'll dig out the relevant Acts if you wish.
But the "changes" were marketed as clarification, and I'd agree that they did little or nothing to clarify the public's perception of where the line is, and will make little or no change to the outcomes, either in CPS charging decisions, or in all likelihood, jury verdicts.
If, as has happened, the bar has moved from reasonable but not disproportionate, to reasonable and even disproportionate but not grossly disproportionate, then the only way it clarifies the public perception is if the public has a clear understanding of, firstly, that nuanced change, and secondly, exactly where the line is between those three states.
The law, therefore, changed, in a very minor way. The real-world effect will be minimal at most because, already, a householder has to go quite a long way over the top to get charged let alone convicted, for reasons of public policy and national interest, if nothing else. That is to say, juries are comprised largely of householders and generally not criminals, and most of the jury are likely to see themselves in the householders shoes, and are naturally sympathetic to burglary victims. The CPS know this all to well, and given the requirement of a "reasonable prospect of conviction" tend to be bring csses to court unless the violence level used is pretty clearly way excessive.
Perhaps the more subtle and beneficial change isn't the headlined one but the slight change of emphasis in, as I'm sure you're fully aware, PACE, and the inferences for investigating officers as to how, when and even where to conduct initial interviews with householders that may have themselves acted criminally violently in overdoing seld-defence, and the requirement to consider evidence that there weren't overdoing it as well as evidence that they were, before defaulting to just nicking them and sorting it out later in a formal interview, thereby perhaps victimising innocent and potentially traumatised householders all over again. It's bad enough being burgled, and perhaps literally fighting for your life, without being banged up in police cells for two nights for not losing the fight.
But on the initial point, yes the law did change. Minimally. I doubt it helped public perception much, and even less helped actually understanding, and I doubt it made much if any difference to outcomes.
It's like getting a high jumper to jump over a three foot bar. If he clears five feet, you can change the bar, raising it to three foot six, but it won't change his outcome. The change in law raised the bar a bit, but the CPS were already clearing it anyway.