History is fickle. What actually happened depends on who's doing the remembering. One example where this is true is in the Jewish history of pre-war Eastern Europe. Was it most frum? Mostly frei? A bit of both?
Depends who you ask. The folks at Artscroll would have you believe that everyone was, at the least, moderately Chareidi while the Gedolim of that time were angels compared to the ones we have today. Meanwhile, Hollywood would have you believe that there were no frum Jews, or just a very few, while the nearly total majority of Jews were regular, secular citizens. The truth, as always, is somewhere in-between.
One thing is certain. In Eastern Europe, Jewish cultural life was much stronger than in North America due to a few factors. One was the always pervasive anti-Semitism of the surrounding populations. There were also residency restrictions leading to the creation of large Jewish neighbourhoods and shtetlach. As a result, Jewish populations were much larger and culturally vibrant than the fragmented communities we have today in many places outside Israel and the Greater New York area.
What does that mean? Well, one of the common myths spread by the activitist non-frum nowadays is that the reason Torah observance didn't take off in America until after the war was because before then it was all the non-religious Jews who were fleeing rabbinical oppression that were making their way to America and that they would drop their Judaism like a bad habit once they reached Ellis Island. Now while a minority of Jews might have felt this way, it is clear from history that the majority of Jews seeking a new life in North America didn't.
Rather, what conspired against them was a lack of education and support structures in their new homes. See, what made Eastern Europe special was that Judaism was everywhere. It was part of the landscape which made it stick out as an oddity far less. Even uneducated Jews knew where to buy their meat, where to go to shul on Shabbos and pretty much everyone got at least a basic cheder education even if they didn't personally observe much later in life. In North America, this was absent, so the same Jews who had been Jewish by osmosis in Europe absorbed the secular culture of the surrounding society instead.
It is this Jewish middle class, the Jews who aren't particularly observant but who respect tradition, know how many sides a humantaschen had, and can hum the first few bars of Kol Nidre, that has dwindled in the last few decades. As society around us continues to radicalize and assimilation continues to devastate our numbers, it's getting harder and harder to find non-observant Jews who have a proper respect for Jewish tradition combined with a decent basic Jewish education.
Perhaps this is something that Orthodox outreach programs should concentrate on, instead of their current flawed kiruv approach in which Torah observance is sold as a simplistic, glitzy path to true spirituality. Perhaps it's more important to ensure the vast majority of non-observant Jews know the basics of their heritage instead of trying to sucker well-intentioned customers into a pre-formed black hat model.