Do you have anything to back up your claims or is it just that you'd prefer China not to be involved? Because I've found multiple sources backing up the claim that China was in fact involved.
This one (https://www.businessinsider.com/the-complete-history-of-sush...) goes even further by specifically talking of Southern China as the origin and suggests that the influence of northern invaders explains why you won't find much signs of it in modern China.
I clarify my point about sushi going through China. In the Takamiya's paper, one of the links above, the author discussed the Ocean Road hypothesis. I agree with this hypothesis. It'd be difficult for the food culture to propagate through land. It'd have to pass Northern China which is not much of a rice culture. Japan likely traded with Southern China and South East Asia through sea routes.
Rice arrived to Japan thousands of years ago. At the time, Southern China is not part of present day China. The Baiyue people were good naval navigators. They probably traded with Japan and South East Asia. Saying sushi got to Japan through China is misleading. People would think that sushi travelled through China land to Japan.
Rice arrived to Japan thousands of years ago. At the time, Southern China is not part of present day China. The Baiyue people were good naval navigators. They probably traded with Japan and South East Asia. Saying sushi got to Japan through China is misleading. People would think that sushi travelled through China land to Japan.