Considering that Title 10 (i.e., National Defense Act of 1947) is basically the only logical place to do so, you are right.
And you are right on this part, as well. If they decided to create a definition in Title 1 of the US Code, one that would apply for all the remaining titles, they could do so...even if they wanted to define the Navy as the Land Service. If POTUS would sign such a silly definition, it would apply.
Like it or not.
You have a bizarre anti-American theology.