I agree with virtually everything you say about unnecessary belts on "Magnum" cartridges. However, there is at least one American cartridge which requires a belt to headspace, and that is the .458 Winchester Magnum and its progeny, the Watts, the Lott and the American.

As for a .30/.338 without a belt, take a look sometimes at the .30 Newton, introduced in 1913 as the .30 Adolph Express. It, and its German counterpart the 8X68S are true beltless magnums (as is the largely ignored .284 Winchester).