We also need to look back at the start of the problem: how come so many Jews became anti-religious? In part, it was the influence of the times; amei haaretz who previously would be part of the Jewish community now had a choice to leave; and attractive influence of various isms.
But, we also need to admit that Jewish communities, and Talmidei Chachamim, did not initially have effective tools to upheld Judaism, it took some time to develop these tools – and by this time so many Yidden became members of various movements … One can say that adequate response was early developed by R Hirsh (and attempted before by Mendelssohn), R Salanter, Beis Yaakov movement, but really developed after WW2 both in Israel and US. During 1930s, Chofetz Chaim writes a lot about problems but offers almost no solutions, except “keep at least one cheder in each town so those who still want would be able to send kids there”. He even pleads with Polish President to rescind sanitation requirements on the mikvaot because Jewish communities were not able to abide by them…
So, two major approaches survived: (1) going to the desert to avoid any contact with anything “modern” and (2) developing approach that allows people to understand modernity in the Jewish context. After about 80 years, I would say approach (1) had definite successes “in the short term” by creating large community with large families of those previously committed, and (2) had definite success attracting more assimilated and educated people. At some point, we should get out of survival mode and ask the question – is Hashem looking for a nation that reads old books or a nation that reacts to the world that He sent us to.