Yitayningwut: I’m not well versed in all siforim chitzonim, but I can still vouch that the Diveikus concept in unique to Judaism. Maybe you don’t understand it well. The Deveikus concept means that the Jewish people are “One” with God. This means more than just connected occasionaly; it means that God, the Torah and Israel are Kaviyachol ONE ESSENCE. This is famously stated explicitly in the Zohar Hakodosh “Yisroel V’Orayasa V’Kudsha Brich Hu Chad Hu”, meaning ONE entity Kaviyochol. I highly doubt you will find any secular source matching this concept.
As far as Litvish Hashkafa is concerned; first, you are mixing up the term Hashkafa with the term Machshava. Of course Litvaks have their Hashkafa. Hashkafa means outlook; every sect within Jewry have their own unique outlook of Judaism. You are also mixing up the concept of independent Diveikus with Hashem unconnected to Torah learning, to the concept of natural Diveikus with Hashem through Torah learning. The former is what your rebbe meant is not your concern; however the latter is the central and fundemental foundation of Litvish Mahalach/Hashkafa [call it whatever you want].
I don’t really see a point in continuing my conversation with you, since you are just evading my points.