Once steel reaches plastic elongation, there's no further gain in tensile strength to be had, so you have to design respecting the limit of elastic deformation either way. Then you apply working safety factors, but i don't see why they would be any different unless the tensile strength of CF was more intrinsically variable than steel - it isn't tmk. And of course, it has quite different properties anyway so it's never going to be like-for-like in design.
Your point about inspection and detection of defects is correct. But after a generation or two of commercial development of Composites and CF manufacturing techniques there are other ways to monitor structural health appropriate to the material: Airbus 350 and Boeing 787 have composite fuselages etc and they will reliably detect any defect in the laminate in good time, I certainly hope they will.