Demo does not really fill the role of crowd control: http://en.wikipedia.org/wiki/Crowd_control_(video_gaming). According to that page, pyro is CC, not demoman.

In HL, the role of Area Denial is filled by many classes already. His role in HL is dealing damage alongside the heavy. Thats it.

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"He is the first to the midfight because of the high damage he can do"

This is not what because means.

Talk:Demoman