Torah – Still holds true. Seen by the walls and seen by people. If I covered my hair with wide mesh, it wouldn’t be covered halachically.
popa – Two separate issues. YOUR hair can’t be seen is not the same as ‘people shouldn’t see hair when they look at you’. If you are bald, I don’t think you are required to wear anything, and along those same lines I know most poskim hold that you cannot wear a sheital of your own hair unless it was cut before you were married.
I was raised in a world where people covered most of their hair, not all, and I spent a very long time discussing this issue with a Rav before my wedding. I needed to be convinced that is was necessary as well as right. I do have my issues with sheitals on a personal level, though, and do not wear them anymore. Neither does my wife.