R Yitzhak Adlerstein brings aq quote from Michtav Me-Eliyahu vol.3 pgs 355-360. – R Hirsh’d system in Germany produced observant Yidden but no Talmidei Chachamim. Eastern Europe with Torah-only education produced a lot of Talmidei Chachamim but at the expense of tremendous drop out rate from observance. An anonymous wrote a response in 1960s questioning the downside of German system:
The upshot of all this is that the claim that the Frankfurt approach was not capable of transforming gifted students into geonim in Torah is erroneous. It is certainly true that gifted students suffer no loss of talent by engaging in increased study. Thus, quite the contrary to the extent they increase their secular study, their minds are broadened and their Torah studies are deepened proportionately, so long as they truly study for the sake of Heaven. On the other hand, a student lacking in intelligence, who is also denied exposure to secular study, will hardly grow in Torah and become a distinguished gaon due to that denial alone. R. Baruch of Shklov [the talmid of the Gra]…states: “There are Jews who are bereft of intelligence and secular study, which is precisely why they denigrate the wisdom and knowledge they lack. Moreover, they hurl accusations of heresy against the wise, so that they be stigmatized and viewed as outcasts by the masses… Had not R. Samson Raphael Hirsch established this approach for us, we would not dare to expropriate it without the prior approval of the roshei ha-yeshiva and gedolei ha-Torah of our generation. But since R. Samson Raphael Hirsch merited producing several generations…all who follow this path walk in a well-trodden path and drink from a well dug by experts. Those who, for the sake of Heaven, oppose this approach must admit that such a ban on secular study in our time and in our countries [i.e. in contradistinction to Israel, as he writes later] would be a “decree that the majority of the community could not comply with… It seems to me that both [i.e. the approach that allows secular study, and the one that does not] educational approaches are well-grounded in the sources, and both are essential for the continued existence of the Jewish people in our time. So it shall remain until the redemption takes place.