Funny you mention old Japanese cars, as mine was stolen (and subsequently found) just a few days ago.
90's era Japanese cars are notoriously easy to steal, and the only thing that stopped them was the immobiliser kicking back on. When they initially took it, the immobiliser was off thanks to a mistake on my part, but it automatically re-activates when the car is turned off.
To get it home after it was found, I actually started it with a plastic spoon thanks to the minor "productivity hacks" they had applied to it. Keyless start!
The window and door were fine, because all you need to get into the door is a coat hanger down the window sil.
Given enough time, I suspect they would have gotten through the immobiliser fairly easily, and I honestly don't think a kill switch would slow them down much either as to be convenient, they need to be in the cabin.
My last car had a kill switch, and it was a big red button underneath the steering column. They're going to figure it out, but it might slow them down enough to consider giving up.
Car alarms are next to useless, no one cares or checks, but a good immobiliser will at least push it past the "easy grab" realm of opportunity. Unfortunately not until after they've broken in, taken your stuff and broken your key barrel though.