Feif said his RWMO community, although they don’t officially condone women with uncovered hair and pants, some women in his community do publicly go as such. In a LWMO community it is officially condoned.
In ANY Chareidi community — Yeshivish/Litvish, Chasidish, etc. — it is virtually unheard of for a married female community member to go with uncovered hair and/or pants. Doing so would clearly put someone outside of the community. (Unlike in the RWMO, such as Feif’s example, where it isn’t officially sanctioned, but they are accepted in shul and in the community as such.)
There are dozens of other similar examples.
Clearly MO (whether RW or LW) are more closely aligned to each other, while Chareidim (whether Litvish or Chasidish) are more closely aligned to each other. Much much more so than MO to Chareidi.
Using these groupings, clearly OTD is a much much more prevalent problem among MO than Chareidim. And your example of most of your MO classmates becoming frei, is a living example.