My 2 cents to add: AFAIK Belz preceded Lubavitch in kiruv in Europe and My Rebbe bemoaned the fact that changed.
I heard an apparently true story joke recently although I can’t personally verify for obvious reasons. Still the point is illustrating at least. a certain Rosh Yeshiva forbade his bochurim from learning Tanya. So they prepared a list of a few prakim for the RY to look at so as not to waste his time and still make an honest assessment. The next morning they asked his opinion on it. “It’s all about Hashem but where’s the Torah?”
For the ignorant, Tanya references many many sources brilliantly but doesn’t spell them out in footnotes, as The Alter Rebbe sufficed with a brief explanatory note in the beginning that is a collection of sources (apparently they knew more sources back in the day). But that actually isn’t even the irony.