Far Horizon
your points are well taken re: safety margins.
Over building Al bikes to get the safety marginresults in a very stiff unforgiving ride. Its not inherent in the aluminum its just the way its built. Although aluminum does not have the fatigue strength of stee l- that is inherent in the material.

Carbon fibre - I just don't trust it. Too many weird unexplained catastrophic failures for me. (like my expensive brand new ski pole)