IJA wasn't that extreme bad, their downfall at Guadalcanal was ultimately the result of losing the Battle of the Coral Sea and Battle of Midway. Without air superiority it is impossible to keep up with supply line and bring heavy equipment onto the islands. They could only supply their troops at night with fast destroyers and it was very inefficient. Their munition was soaked rendering useless, their heavy artillery cannot be brought onto the island. IJN battleship artillery cannot support at daytime. Medical and food supply was always shortage while the crazy Pacific weather keeps happening. How can you expect they can fight well? They lost at Guadalcanal just like Germany losing in Stalingrad.
Consider their victory in the Battle of Singapore in spite the Commonwealth forces 3:1 outnumbered them, how much casualty of the USMC they inflicted in Iwo Jima and Okinawa, under the condition of total annihilation of IJN. I don't agree IJA was 100% trash.
Assume we are discussing IJA in late-1944 to 1945 and assume they are no hundreds of USN aircraft carriers floating around in the Pacific,
- assume they didn't do full retarded WW1-style banzai blob charge because you are the commander
- they did have real tanks, they saved those for the "final decisive battle" for the home island
- they did have screck-like infantry AT weapon, copied from US zooka and German screck data, ofc
- IJN can bring battleship heavy artillery support and Zero strafing, with or without kamikaze
- assume we were fine with COH1 German "laser-glided" V1 pin-point accuracy, IJN can do the same with their "manned-V1" Ooka
- they actually purchased Panther and Tiger from Germany, assume those reached Japan unscathed