Was the Second Sino-Japanese War merely a proxy war?

Was the Second Sino-Japanese War mainly a proxy or backwater theater of the Second World War?

No. Foreign involvement did not make it merely a proxy conflict, and Chinese forces fought active campaigns including in Burma.

The audience proposes treating the Second Sino-Japanese War as a proxy or backwater theater within the wider world war. That description is too narrow. Calling the front a static guerrilla conflict understates both the scale of Chinese resistance and its connection to other Asian theaters. Chinese forces also fought the Japanese in Burma, showing that their war effort extended beyond a single immobile front.