Claiming R’ Chaim Kanievski is only paskening that way for Bnei Brak does not help much.
A person who doesn’t know that the whole world considers him their posek is not humble, he is stupid. And a person who knows that the whole world considers them their posek should not be reckless and issue unqualified psakim like this which will be thought by laypeople to apply universally while in reality only apply only to their little hamlet. They should clearly specify as such. As a wise person once said, ?????, ????? ???????, ??? ????? ???? ???? ????? ????? ??? ?????, ????? ???????? ????? ?????? ??????, ????? ?? ???? ?????.
Being that I assume R’ Chaim to be neither stupid nor reckless, I assume that either he actually is of the opinion that this applies universally, or someone using his name is, and their logic is probably somewhere along the lines of the Rashba that has been mentioned here.
At any rate, when you learn the sugya, the pashtus is that this halacha does change with the times.