A primary reason to upgrade to a C100 (any version), or, any camcorder, is the ergonomics of shooting it vs. any DSLR.
The list of ergo advantage (off the top of my head, halfway through the first cup of coffee!):
Side handle and strap for eye-level, low, and high-angle hand-held shooting support with the right hand. A big red button on it - start/stop recording.
Top handle for secure handling.
XLR audio inputs and decent preamps/recording gets you into the world of pro audio. Not just mics, but mixers of all types.
The control surface on the left side of the cam - many hardware buttons for commonly needed functions. You won't be diving into menus in the middle of a shoot.
Built-in ND filters.
Multiple methods of monitoring exposure, including a waveform monitor display.
A tilting LCD monitor - supports shooting at high/low angles. (limited on the Mark 1, IIRC).
Clean outputs for external recording at higher standards.
C100 Mark 1 DPAF adds the first camcorder AF that is actually useful for something in pro shooting!
C100 Mark 2 includes slight improvements to AF, but also much better monitoring.
All these cams are bigger than your 7D.
IMO, they are *vastly* better than a 7D; but that's because I value all those functions listed above very highly. How would you value them? Maybe not the same...
Shooting a DSLR can yield comparable image quality, but the ergonomics make that quality more accessible in a cinematography approach to shooting (you're in control of the set). Shooting a camcorder like the C100 series gives you more consistency in creating quality imagery, not only in cinematography, but also with videography (you're not in control of the set).
I *strongly* agree with you that Canon's latest pricing ($2,500 for a C100m1, $3k for C100m1DPAF, $4.5k for C100m2) makes a true video camcorder of very high quality more affordable than ever. For my money, that's the great AF and better monitoring of the Mark 2, that's less than $200/mo. at Canon's 0% 24-month financing.
And, of course, use all the nice canon glass you have, though the STM zooms enable face-detection and tracking with DPAF.
From the upper left corner of the U.S.
Photos, Video & Pano r us.
College and workshop instructor in video and audio.
70D, Sigma 8mm, Tokina f2.8 11-16, Canon EF-S f2.8 17-55, Sigma f2.8 50-150 EX OS, Tamron 150-600VC. Gigapan Epic Pro, Nodal Ninja 5 & R10.