My cultural learning experiences began watching my Swedish grandmother cook. We lived in a broader immigrant community of Northern and Southern Europeans, becoming quite prosperous working in the deep pit iron ore mines.
To keep their husband’s well fed, the Northern Europeans adapted the Cornish pasty–meat and potatoes wrapped in a pastry shell–into our own UP Michigan pasty. I didn’t experience the Cornish kind until decades later in Pasadena:
A rumination. What you call cultural fusion seems to me to be increased diversity. In a bit of irony, as restaurant offerings become more diverse, the classic USA coffee shop seems to be endangered. I loved Walter’s when it was a coffee shop. I especially liked the Dagwood burger.
We ate the other night at a spot I do view as true fusion, Loro. It is the pairing of Aaron Franklin and Tyson Cole styles. The flavors of Franklin Texas barbecue and the Japanese genius displayed in Uchi are melded. Even the architecture blends the Texas barbecue joint and the beamed architecture of larger Japanese buildings. My other fusion favorite is Chi’lantro, blending Korean, Mexican, and a nod to barbecue.
Yum. They sadly discontinued my favorite, the bulgogi burger. Bulgogi, onion (grilled), lettuce, tomato, a wonderful spicy mayonnaise sauce, caramelized kimchi, and a fried egg. Their kimchi fries are also good.
What’s missing from the two places you’ve cited, IMO, are the changes over the years–more evident in single restaurants like Walters. My home town pasty place managed to fuse in the Italian tradition–but it took 50 years.