Bootcamp failing with "cannot create partion" and corrupting APFS container
My issue turned out to be Fusion drive issues that necessitated doing a diskutil resetFusion and blowing EVERYTHING away, recreate the APFS container, and reload. Painful, but I now have a Windows partition running. And yes, Bootcamp Assistant totally ignored everything but the APFS container.
Closest thing I could find to my issue: https://support.apple.com/en-us/HT207584