This defence was introduced in 2010, partially as a defence for victims of abuse who lose their control due to a serious fear of violence. And what we have here is unintended consequences of a well meaning piece of legislation.
This is important I think because people often get upset when cases don't have quite the outcomes they think they ought to, and then they want to somehow add rules or tweak things to make sure they do.
But changes are not going to have only that one effect.
What people really seem to struggle with in cases like this one is that it is so difficult to prove intent, even when the jury thinks something likely happened with intent. And the fact that the presumption of innocence always means there is a good chance many guilty people will be found innocent.
But changing those basic elements of the legal system would have all kinds of systemic effects, some of them pretty horrible.