New EOS 5D Mk III Video
The problem seems to be the way Canon firmware stores images, large or small. As if it uses a too high unsharp mask threshold combined with a too large radius, causing a soft look with halos. If you change the sharpening level most likely only the strength changes.
Canon knows how to do it right in DPP. It should be fixable with a firmware update. Problem is that apparently not enough people complained about it since their early DSLRs.... Let us all start a campaign demanding a fix!