N0m,
Either you are a Lubavicher who has been inculcated with all their fraudulent claims, or you are just being very naive. Saying that practically every Jew in Europe (Why Europe davka? Don’t know.) is descended from Dovid Hamelech may be correct, but that doesn’t make someone qualify as DEFINITELY descended, which is a pre-requisite for Mashiach.
As to the claim that he was “unique in his vast knowledge” and that “the bnei yeshiva of today considered him the biggest lamdan among all the Rebbes” – do you have a basis for that other than hearsay? Have you ever heard of the Klausenberger Rebbe zt”l who would darshen in lomdus for hours at a time? And the Satmarer and Vizhnitzer Rebbes zt”l? That is to name just a few.
There are and were a lot of Chassidishe Rebbes who were HUGE talmidei chachomim, but who didn’t spend time displaying it. It often came to light only when circumstances forced them to reveal it.
And as I have pointed out in the past on earlier threads, the “geonus” of the Lubavicher rebbe was often clearly faulty and seen as such by the same bnei yeshiva you mention. Two examples, his sevara for not sleeping in a sukkah, and the need to convince goyim to keep 7 mitzvos.