It's fundamentally unfair to deny carry permits for decades and then also fail at effective policing.
Most murderers have already committed a lot of crimes, sometimes including other murders. If the police are ineffective many won't be known or reported, but I will hazard a guess that the attacker did commit them. In other words, the effective police+DA could have prevented the stabbing and didn't.
It sucks that the answer is to shoot criminals rather than prosecute them. But that is what the answer will be in the world of ineffective police+DA after Bruen. And frankly, it's good that the option will be there as a last resort for vulnerable citizens.
I know people will suggest all kinds of "better options". But those better options have been known for a long time and nothing has been done. The victims are just a statistic... collateral damage of politics.