Video is there because it is cheap to implement in a camera with live view capability. DSLR video was and is not meant to replace a real video camera. It just happened that the quality is good, DOF is shallow (shallower than in real 35 mm movie cameras even) and the camera is practically free compared to previous cameras offering something similar in looks and quality, like 20-50 times cheaper. So the popularity of DSLR video was quite unexpected. If somebody thinks 5D3 or D800 is also a great home video camera they have been mislead or do not understand anything about video.
I use 5D2 for for certain types of videos, precisely for the movie like effects with shallow DOF. Shooting is done movie style, dollies, focus puller (when needed) etc. Or as a stationary B-camera for interviews, which are shot with XF305 to simplify things and get good synched audio. For fast documentary and ENG style stuff DSLRs are just about useless, but some photographers have to use them, because they have them and because cameras have video they now have to deliver video also, and carrying a proper video cam also would make things too complicated.