Upvote:-1
The question about the timetable is difficult to answer. However, the question lagging behind could be clearly answered: your second hypothesis is true.
The battle of Guadalacanal was fought by the Japanese mainly with forces numerrically inferior to the American marines based on the island. The top number was 20 000 during what is called the Battle of Henderson Field (but is, in reality, the terrestrial part of the naval battle of Santa Cruz). Compare this top number in Guadalcanal to the 100 000 men in Rabaul and you see that the problem was mainly about having enough soldiers at the same time on Guadalcanal, and this problem lied in the Japanese naval logistic.
For the battle of New Guinea, this is a similar issue: at first, the battle w as a matter of small forces whose number was limited by the logistic in the central mountains of New Guinea. Later on, the Japanese had to defend their bases on the North Coast of New Guinea, and they failed because those bases were cut off from Rabaul and other bases that could provide them with reinforcements.
Eventually, why were there so many men in Rabaul? For two reasons: