I don't think I ever suggested that one should bust CAS while awaiting an IFR clearance. That would be a pretty stupid thing to do.
Statistically speaking, you should be quite safe doing that. In CAS, all traffic is separated both horizontally and vertically by wide margins of safety, so passing randomly through it is like a neutrino fling through a crystal lattice... the chances of hitting something are very low. Not so in uncontrolled airspace where all traffic is squeezed into a thin layer of airspace, sometimes only 1000ft thick and pilots tend to route (for whatever reason?) via neuralgic points like VORS and reporting points instead of taking the straight line from A to B. Yet you are right, not many (if any) collisions have happened between instrument traffic in uncontrolled airspace.