I spent a Shabbos in Cedarhurst for a simcha last year. I thought that everyone there bought their clothes on sale – 50% off!
Not everyone in 5T has this problem. I was at a wedding last week for a cousin from Woodmere, and I was pleased that hardly anyone was not dressed tzniusdik.
At a different wedding at the same hall just one month earlier where the Kallah was also from the 5T, the Mesader Kiddushin under the Chuppah actually waited until they draped a shmattah over the Kallah’s shoulders before saying the Brocha – that’s how undressed she was (and how frum he was B”H)! I was in the back and didn’t realize what was going on, but my wife and daughter filled me in afterwards. I stayed on the Men’s side and never looked at the Kallah, but apparently her dress was SLEEVELESS and BACKLESS!
Oy. I don’t think there is any Orthodox sect that pretends that such a thing is acceptable, no matter how modern.