The o-ring was still the weak link, a small part that decision makers assumed was insignificant whose failure caused the complete destruction of a massive system and tragic deaths. The organizational failures are just why the weak link wasn't addressed. We can say with hindsight that things should have been better communicated and the warnings should have been heeded, but the fact is they were dealing with a complex system where the risk was sufficiently non-obvious that they could disregard the warnings.