OK, after more searching I found this answer form the same helpful author.
He says that when the qml files aren't in the root folder you should add
import "qrc:/QML in the main file so it could see other components in the qrc file. (This path is specfic to my case because my qml files are in ./qml folder.)
On thing to note that might seem obvious but I spent quite a few tries to figure it out is that you must compile the qrc file
to py after every change you make to the qml files.
Meaning running pyside2-rcc qml.qrc -o qml_rc.py. Otherwise the imports won't update, and you'll be stuck trying to figure out why the changes you're making don't affect anything.