Aaa, yo – argue with the chazon ish.
Yemenites didn’t have yeshivos either, but they all were learned. Most sefardi immigrants were not, and were in spiritual danger, as attested to by the gadol hador.
In the times of the rishonim, this was the opposite; sefardim wete, by and large, more into learning than ashkenazim.
Having to deal with the haskalah only made litvishe yidden learn less – before it, the baalei batim would learn for hours and hours a day, as I’ve seen in town records from my grandfather’s yeshiva town.
Drop the narrative about what caused what and just look at what the chazon ish saw – he saw better than you and me.