The Chofetz Chaim lamented that breaches in tznius were common in his time, too. That doesn’t mean there’s any justification for such breaches. And when the Aruch Hashulchan and Ben Ish Chai lament that it was common that some didn’t cover their hair, they very much condemn that flagarant violation of Halacha. So your use of the Aruch Hashulchan is very much disingenuous as the A”H is saying the exact opposite of what you’re trying to claim. Namely, he specifically writes it is a terrible aveira to leave the hair uncovered.
I am familiar with one Rov who there’s a picture of from about 80 years ago where his wife’s hair allegedly wasn’t covered. Even assuming that was the case, when he was the yungerman when that photo was taken was long before he because a big rabbi in his community. I don’t believe he was even a pulpit Rabbi yet at the time; He certainly wasn’t a godol then and his wife’s action then, assuming that’s what happened, aren’t by definition a demonstration of what is or isn’t permitted under Halacha.