Jude- there were many Tzaddikim in pre war Europe outside of lubavitch. Lubavitch doesn’t believe in excluding others from being leaders and even Tzaddikim in klal Yisrael. The Rebbe met with, and highly respected, many admurim/ Sephardic chief rabbi/ etc etc titles.
Just happens to be that I don’t hear of any “Tzaddikim of Tanya” Today outside of the Rebbe, who by the way saw yidden who came to him from all streams of Yiddishkeit- not just lubavitch in case you were wondering
(Just cuz you’re gonna ask- yea there is only one nossi hador- nossi as in Neshama klalis of the gen, sorry it’s not popular… every stream in Yiddishkeit has something special and unique they contribute)