Great test! If I take your full rez and downsample it so that it matches the video shot it exhibits the very same effect that I first noticed when investigating this. The video side doesn't look too bad until you compare it with what it should be like and you can see what is missing.
None of us users, really knows what goes on inside the camera. I'm sure the Canon softens and lines skips and somehow makes a a 20 megapixel sensor a lot less for video, because sometimes we see moire or artifacts.
But heck it's a $2,500 camera that shoots good motion and great stills, so it's kind of hard to complain about it.
Then again I don't know why our RED One with the MX sensor is 4k and with the Epic 5k. I guess it's processing power, though something is getting tossed, but in reality all I care about is the final look.
We've used stills from our RED One in print and usually they're fine as long as the subject is waist up. Full length on a horizontal format becomes more challenged, but I'm not 1000% convinced that one camera can do everything anyway, for still or motion projects.
We primarily shoot the RED, but until we get an Epic, it's a beast and the 5d is a great camera for quick set ups, tight quarters like a quick window mount and low low light.
We're also adding that Sony FX 100 or 1000 or whatever it's called because it does some things the 5d/7d/ and the RED don't do. though once again, the A camera is usually the RED.
Every camera has limitations. The RED has good resolution and a thick file though it requires a more thoughtful professional approach to shooting, the Sony is fast and runs for 10 hours but it takes care in shooting not to blow highlights and some post work to make it un video looking, the 5d can be amazing or awful depending on the subject. Also the 5d2 can get hot and degrade the image so care has to be taken in how long you run a series of sequences.
To match our cameras the one thing that seems to help is to go to ziess lenses all around. I can visibly see more detail and sharpness from that change that anything else.
What I don't think the original poster realizes is the smaller cameras usually shoot 8 to 10 bits, and are 4:1:1 or 4:2:2 where the RED is 12 bits and 4:4:4. Also in any common NLE it all goes back to 10 bits.
I also don't think he realizes that even if you drop 50 grand that's not a lot in the motion imaging world. Not for a camera, heck not for anything.
I can't show it because our last few projects haven't been released, though the client selected 16 still images from the RED and after post production and some retouching, anyone would be hard pressed to know if they were shot with a still or motion camera.