I've owned my Canon C100 for over a year and it's been nothing less than spectacular. I think that people forget that Canon is a business and will likely be releasing the next C300 soon. If they were to give the C100 Mk II Internal 4K and 120 fps for $5500 then how would they expect to sell any of the new C300s?
The image quality from the current C100 is outstanding, low light performance is fantastic, and it's the most reliable camera I've ever owned. The GH4 doesn't have good low light capabilities, doesn't have NDs, and has a smaller M43 sensor. The A7S has horrible rolling shutter, no XLR inputs, and bad moire. Every camera has their strengths and weakness so if you don't want to buy a C100 buy another imperfect camera and live with the results. There's not use bashing Canon as a company just because they didn't call you up to find out how they can sell more cameras.