spam musubi

That's sushi with spam. I wouldn't call that unique because how similar it is to any other sushi, its just an ingredient replacement. Now if the spam was specifically seasoned or prepared then yeah, it'd be a unique snack.

Frybread is basically hungarian lángos

And deep fried podpłomyk recipe is also very similar.

loco moco

I can't find anything like it, or from similar ingredients, so I'd call it unique. They are similar dishes, but either with more than 1 ingredient removed, or lacking the complexity.

cheese zombies, jojos, Seattle dog, huckleberry everything, etc.

Grilled cheese sandwich, potato wedges, hot dog with a different ingredient, huckleberry is an ingredient, not a dish.

Southwest USA and Mexican have a lot of overlap but are also just as distinct with “Tex-mex” being it’s own culinary thing. Puffy tacos, chili con queso, cornbread, cowboy caviar, nachos, etc.

Igredient replacement, literally not a dish but a dip, Native American, a bean salad, nachos are Mexican. Tex-mex I think is mostly one ingredient replacement. Literally you had a lot of beef and cheese and that's how you made Mexican recipes.

Midwest, Alaskan, southern, east-coast, Puerto Rican

Midwest and Alaskan, as well as east-coast, those three sound most promising. Can you maybe tell a bit more about them?

Southern is likely to be European cuisine with one ingredient replacement, Puerto Rico is famously a territory of the USA, but not a state :-)

pasta is any less “Italian” despite it just being Chinese noodles with a few changed ingredients.

Yeah, pasta is not a unique Italian dish. It was invented by so many cultures independently. Bolognese sauce on the other hand is, as I can't find any other similar dish that was invented independently from it. Do you see the distinction I'm looking for?

Edit: you might wonder why then I count pumpkin pie as a unique - the main ingredient changed, and you often add caramel and pecan pies on top, making it significantly different than other pies.