In the air, the Japs had superior aircraft at that time.
At Sea, their surface ships were also equal if not superior to American ships of same class.
Their machine guns were crappy and their pistols a joke. Tanks were irrelavent. Although their artillery wasn't first rate, it was OK, and their cruisers and battleships made up for it.
You are, in the field of firearms history what is known as a BS Artist. Japanese machine guns during the battle of Guadalcanal weren't "crappy". They were odd-looking to Western eyes but they were good, serviceable designs that acquitted themselves well - too well. The Type 92 and the Type 96 "Nambu" in particular were deadly and reliable. Japanese pistols were good designs too but in an ineffective caliber compared to the .45. The Imperial Japanese Army had excellent light howitzers and best of all, the 50mm grenade projector also known as the "Knee Mortar". According to analysis made after the war, it accounted for 60% of all of our infantry casualties against the Japanese in WW II.
Pump shotguns had zero to negligible effect during any of the battles.
The difference was that the US forces seized the key terrain around the airfield and organized effective defenses. The Japanese underestimated the numbers and quality of the US forces and expended their men in futile and wasteful mass attacks. The 37mm canister round was particularly useful during these attacks.
Both sides had high-quality troops but the Americans had the ground and the enemy had to punch through long reaches of very tough terrain to get to our defenses and by the time they reached our perimeters, they were unable to effectively coordinate their actions and breach the defenses. We were also supported by excellent artillery made up of 75mm and 105mm howitzers that were well directed and courageously served. In the end, disease and starvation thinned the rest of them out and we held the field.
Try not to make simplistic statements about weapons - without first doing the research.