My take: Sony has a lot (A LOT) of work to do before they can compete with Canon's ease of use. In run and gun situations the C100 is clutch because Canon designs a smart user interface. Sony's menus are a mess! That said...
I am currently on assignment in Brazil documenting a global immersion course. I am working alone, shooting video and stills. I chose to leave the C100 behind and opt for the A7Sii as I wanted a camera that would draw less attention. I figured the built in stabilizer would allow me to run hand-held more often as well, which is not recommended with the C100. AND it shoots stills, so I can leave my DSLR at home (no stills with C100).
So far I've really enjoyed the size and weight of the Sony. I'm using a Zeiss 24-70 stabilized lens, which couples nicely with the built in stabilizer. It's not as smooth as a MOVI or Ronin, but hell, it practically fits in my pocket!
I only carry one filter, a circular polo, and I adjust my ISO to taste as needed. I have a hot shoe mounted micro rode mic that is good enough for my needs. Sit down interviews are captured with a wireless lav into my zoom. I brought a $200 MePhoto travel tripod. Far too light for the C100 but works fine for the A7S. Overall the setup is brilliant because it is so damn tiny. However, I have yet to master quickly switching between stills and video, mainly because of how clunky the UX is organized.
In Conclusion: Test them both. I shoot with both and prefer each camera for completely different reasons. Because I'm alone on this trip, the A7Sii has been a real savior. It kills inside a vehicle (C100 sucks in cars, too bulky) and it is bananas to have such a decently stabilized unit that's lighter than any canon DSLR. Lucky for me I'm not shooting loads of interviews or I would be hauling out the zoom (same size as the camera!) and wishing I had my C100. The ability to capture stills is nice but I do not prefer this camera to my 5Dmarkiii for still photography. And everyone is peeing in their pants about the low light capability of the Sony. I personally don't see the appeal, it gets very noisy quicker than you'd expect. Turn the lights on, it's much more efficient!
Side Note: I got to play with the FS5 recently. This one is legit. Super light weight and feels great to hold while shooting. A contender for sure! Canon had better start innovating.