Those are flimsy ridiculous theories, and as usual you quote scholars on the periphery not mainstream scholarship. That does not explain that plethora of Paekhe artifacts that are all over Japan. It should be noted, there is zero archeological or historical evidence in Korea to indicate ever that it was conquered by Wa. However, there are tons of early Koreanic art and architecture in Japan which indicate the exact opposite. I refer you to the book by the Covells.

Not only that it is logistically impossible because at the time Wa was technology primitive whereas Korea very advanced technogologically in terms of use of metal weaponry and horses to conduct relatively modern warfare. In fact, Korean introduced experimentation with regard to metals and horses to Japan. How does a country with lack of sophisticated weaponry conquer a country like Korea which already very sophisticated metal workers as indicated by the examples of Silla, Gaya, Paekje artifact I've linked above? In fact, to acquire this modern weaponry, Wa had to import technology from Korea. It even is recorded in Nihongi that early Japan was dependent on trade with Korea for import of modern techonogy. Half of the Nihongi is dedicated to entries on Korea. Hence, it is logically and logistically impossible and it is a dream that is conjured by Japanese nationalists to reconcile to the fact that there are TONS of early Koreans artifacts from Silla, Gaya, Paekje littered all over the Japonic islands.

Also, with regard to Southern Chinese contributing to Yayoi. I doubt that. Both Koreans and Japanese do not share DNA with Southern Chinese. In fact, Japanese and Southern Chinese DNA differ extremely. Hence, there is no genetic evidence and the exact opposite can be inferred: Southern Chinese had little contribution to the peopling of Japan, if any. I will link the genetic study on this upon request.