::::- , I am liking your suggestion, though I'd suggest re-arranging to "Buddhism is divided into two main branches, Theravada and Mahayana, with the latter further subdivided into East Asian and Tibetan branches."  IMHO this is both marginally easier to follow, as well as chronologically correct for those readers thinking in those terms.  
 ::::- Is "East Asian" the best term here? I think that we'll need to explain this for lay readers. (Fine with me if it is the best term.) 
 ::::- We also may want to toss in something along the lines of "Buddhism is divided by scholars into ..." or "Buddhologists divide Buddhism into ..." (Italics only for emphasis here - not suggesting we include in article text.) Dunno if this would really be helpful or not. 
 ::::