God dang it, after spending two hours looking at this, as soon as I created this post and had a coffee, I found my mistake.
I have to check inside of the widget metadata to see the widget and not just inside of the item page…
sorry seems like the issue was between the chair and the screen!
Edit #3: the other part of my problem, the difference between the list widget and the default one, is elegantly explained by @JustinG on the post below.
Thank you!
You just need both the standalone and the list widget. These two metadatas are different. The semantic cards and group lists use the list item widget. The item details page and semantic model items pane use the standalone widget.
AHHHhHhhHhHhhH
/bangsHeadOnDesk
That, and my last edit answers everything…. Why didn’t I find that anywhere on the documentation?
That’s it folks, never work on your smart home when sleep deprived 
thank you @JustinG so much.
It’s summarized here in the getting started section,
but your’e right, it’s perhaps not as explicit as it could be. I don’t recall if it’s anywhere else (it’s been a long week here too 
)
It’s in my long and every growing list of things to address, but it’s all below reworking all the rules docs before 4.0 is released.
Confusion about the difference between the stand alone widget and list item widgets has come up before, though it’s usually someone trying to use a list item as a card
And I honestly don’t know what the default cell widget is actually used for at all.
I went and added the list widget to the semantic model … and it works.
So… like you said, what is it used for??
To my knowledge, there’s only one place. In a layout page when adding a widget, at the bottom of the list of options that comes up, there’s a Add from model option or something like that. If you click on that option when you are adding something to the cell grid of the layout, then the item you selected from the model popup will use it’s default cell widget.