The DF-21D and DF-10's rumored anti-ship versions can threaten the waterway between Japan and South Korea from Shandong. With the overflight of North Korea, China can perpetually attack Japanese and American assets anywhere around Japan from Liaoning using J-10Cs and the new version YJ-83. I think China is not losing anything from not having a coast to the Sea of Japan. Islands in the SCS are a lot more strategic in my opinion.True, but if China had access to Sea of Japan, Japan and SK also would have to divide their resources to the region (Sea of Japan) for potential China + Russia attacking them during crisis, just put a small fleet (1x 055, 3x 052D and 5x 054A and many 056 there) plus strong shore missile defense would make Japan and SK would think 10x to get involved in Taiwan for example
Nobody would even think to have a land attack/invasion on China currently, even not in the last 50 yrs at least anyway