states generally have laws about what level tint you can have and it is usually different (less shady) for windshields compared to sides/rear, and some allow for some portion of the upper windshield to be more tinted. it's a complete mess of differences between states.

warmer states' laws tend to be more lax and allow heavier tints, but not always.

supposedly, the reasonable standard is that a cop is supposed to be able to see the driver's face through the windshield easily and if they can't, they can pull you over and cite you. I say this as someone with a tint job others might construe as illegal and I have my little ways of avoiding scrutiny.

I have never heard someone say that other people should have a type of tint job to mitigate effects from headlights. that person sounds like a bozo and I would tell them to cram it up their cram hole.