To start:
I wouldn't go so high with units, i.e. Army Groups. Remember becuase of Island Hopping, most untis involoved were, at best, regiments, their parent divisions scattered across the pacific.
Mixed native units, Americal, Philippino Scouts, Merril's Maraders.
I'll dig out some of my reserach from college and get back to you.
The Sino-Japanese war was conducted at fairly large scales [Chinese Route Armies and Japanese Armies]. Chinese expanded to Area Armies later in the war.
As far as WWII in the pacific went, you are on the mark. Very few division level operations. Mostly BN, BDE, and RGT level operations.