Hakatan,
Pleas don’t pick and choose. Because the Gedolim didn’t recognize that the world they knew for centuries, millions were lost to death and shmad.
Through the Crusades, blood libels,and pogroms Jew either rebuilt in place or left. In either case it happened as a kahilla and the cummunity was able to go . In addition, Jews stayed frum becasue the only option was conversion.
With the pogroms of the 1880’s, things changed. Many Gedolim advocated that Jews not leave because the oppresion and poverty made it easier to keep Jews frum. What hat changed was that Jews now had options, either the treife medina or the various secular isms ( socialism, anarchism and yes, zionism ).Despite instructins not to go to the treife medina, Jews began leaving in huge numbers. And, because for the first time they were leaving without Rabbanim and without the kihila, many were lost to assimilation. Had the Gedolim recognized that Jews were going to the US anyway and sent rabbanim to guide them, things might have been diffrent. Had they organized mass immigration under their guidance perhaps the Jews killed in WW!, the Russian civil war, the Holocaust or were shmadded by the Comminists after 1917, might have survived.
The Gedolim were great, but they were also human