I had recalled reading that somewhere, but after doing some research,
it appears that the exterior diagonalized tube is is the structural
system in most common use for tall buildings.

What I had earlier read was that some buildings have a concrete
structural core, and the floors are cantilevered from the core.

Thumbs up! I appreciated your reply and I was quite curious myself. I had a little time last night, I did some research and found that Mid-rises may or may not have a core, and that in some instances, the cores ARE structural components, and others not, just like you noted.

All buildings are unique, that's for sure. Thanks for the follow up!