Is communication as a discipline more or less fragmented than other disciplines in the humanities or social sciences (i.e., such as history, psychology or sociology)? Explain and support your opinion.

It's not really possible to argue either side of this with any degree of accuracy without a clear definition of "fragmented" and an agreed upon metric of what constitutes fragmentation. Absent that, one can say that communication studies is similar to many other disciplines in the social sciences in having several subdisciplines and career paths for students.
Some areas of communication, such as rhetoric, are primarily designed for students wishing to pursue advanced degrees, while others, such as public relations, are more strictly vocational. As with many other disciplines, individual university programs vary in whether they offer certain specialties within communication studies or other departments. For example, rhetoric and journalism may be offered in writing studies or English. Journalism can be part of standalone programs and speech disorders may be studied in communication or various health departments.