^Hmm. Sounds like Shane Johnson was thinking of Roddenberry's claim from the TMP novelization but (as is so often the case with human memory) exaggerated it in the retelling. Roddenberry didn't say that all the other Connies were destroyed, just that only the Enterprise
came back from a 5-year mission with both ship and
crew mostly intact. Meaning that sometimes the ship survived but not most of the crew, or most of the crew survived but lost the ship -- and implying that ships that weren't assigned to 5-year missions aren't included.