But would professional cinematographers use DLSR-Bodies at all? Wouldn't they use dedicated movie cameras?
Before the Canon 5D2 people either used HDCAM, film or cameras like the RED, which were notoriously difficult to obtain and make work properly.
The 5D2 was cheap, had a wealth of great glass and had the large sensor look. The likes of the Alexa, the Canon C's the Sony N's & F's all came in the wake of the 5D2, when the sought after large sensor look became widely available.
Now, a professional cinematographer would use a dedicated movie camera, but when the 5D2 came out it was a revelation. Compact form, lightweight. Not without certain caveats and limitations. This is why they were and are used on features and high budget TV work.
Something like a sony f55 costs 1/5th of what a HDCAM cost. THe HDCAM remains better for many situations, but the f55 is better for some others. So now folk are going back to dedicated movie cameras, with proper audio connections and better ergonomics, simple WB procedures etc.
All that said. The best camera in the world needs somebody who understands light to work it, and the pictures need to be cut in a cohesive narrative. Whether its an Alexa or a 600D.