In Germany we have "Störerhaftung" where routerowners are responsible for everything that happens through their router.

I wonder how this would hold up in court, couldn't you argue that routers are generally buggy, how can they force any responsibility if they can easily be hacked?

It would depend on the laws of the jurisdiction. I would imagine if you can show you kept the firmware up to date and had a secure as possible config (eg not having admin interfaces exposed to the internet), you could argue that there's no negligence - outside of maybe using a known insecure vendor; sometimes I think that would be a good idea (cough cough Fortinet).

Germany has some sensible laws about personal responsibility, like it being an offence to run out of gas on the autobahn and seriously treating driving in general as a privilege. But it requires a certain cultural mindset.

Nearly every stock consumer router keeps getting these RCE’s. Perhaps that’s the point, they can get any arbitrary household in trouble if it’s expedient to do so.

It won't work. You would need to back up your claim with proof that someone hacked your router. You can't drive a car that is easily breakable and expect the court to clear you of any responsibility if it causes harm because it broke while you were driving.