It is absolutely fair to say they did not consider security (at least to a level that can be considered real security). They targeted a Orange Book Level C2/Com

It is absolutely fair to say they did not consider security (at least to a level that can be considered real security). They targeted a Orange Book Level C2/Common Criteria EAL4 level of security (at best) which is a level that was not even really intended to indicate there exists any security at all, and, as a result, were permanently unable to retrofit beyond that. They attempted to many times and failed every single time despite decades of effort. There are multiple systems designed both before and after that were designed to achieve the higher levels of security and succeeded. The security designed in was incompetent at the time and incompetent now and, as history has shown us, unfixable. To then address your second point indirectly, I agree that there are systems, such as Windows, that have "security" designed for systems where all agents are inherently trusted. These systems are not inherently worthless as it is perfectly fine to use in situations where security is unnecessary such as children's toys or running a disconnected device. It is, however, unacceptable to use such systems in contexts that require a minimal level of security such as banks and hospitals like how they are used now. Using systems designed only to protect against casual and inadvertent attacks in critical systems is engineering malpractice.