Hi,
Another variable is whether one uses the (default) 'Film standard' curve or a 'Linear response' curve in Capture One, but that was already the case before C1 version 10. The Film curve tends to push apparent exposure by a half to up to a full stop, while the Raw data is still far from clipping. That may cause people to select a less exposed frame from a bracketed series, which will then look relatively dark (because of the relatively under-exposed Raw data) in another application that has no way of knowing how C1 renders the image.
Cheers,
Bart