no you're right, but only to a certain extent. And without camber/caster plate, they can't even be changed much, and I assumed a slight toe-in would be applied regardless of what setup because we're talking about daily driving. I was trying to keep it less technical, and isolate the topic to just wheels and tires, but it seems you're savvy in all.
I think alignment is crucial in handling for lower tier of handling limit, e.g. highway driving, and can only go so far. But the overall balance from sheer contact patch area bias at the car's traction limit (at the track) are mostly affected by staggering of the tires.
I dont know what the scrub radius on our cars is, but changing it less than 20mm I don't think will have too much effect on handling. Im assuming that our cars come with slightly neg SR, thus widening the track should make it more neu. Or even if it was pos/neu to begin with, making it more positive would ultimately give more steering feedback with higher steering effort, which IMO are good. I've tried my car with and without 10mm spacers at the track, but honestly, the feedback and inputs are at such high levels that the SR effects are not really significant. maybe just a taaad bit of increase steering effort.
Edit: I read your comment again; you said "highway stability" which I agree with you that alignment is the primary variable.