well because the IJA/IJN DIDNT have the advantage at every turn...

We can first point out the traditional maxim that a defender in an entrenched, prepared position is already at a great position of superiority over a numerically similar attacker. And once the limited Japanese presence on Tulagi and on Lunga Point was pushed aside, the Marines were given an amount of breathing space to establish a perimeter, it was rarely with enough troops, or something Vandergrift and others felt securely about but defenses were able to be prepared with some care.

But there are several factors which were specific to the fighting on Guadalcanal that doomed Japanese efforts in the end.

1. Lack of air superiority. Japan began the fighting with no usable airfields closer than Rabaul, meaning fighter sweeps and bombing missions had to operate at near max range, limiting room for error or time on target. It also made it so damaged aircraft were that much less likely to make it back, while this would change with time it was still a major handicap.

   This had not doomed previous Japanese offensives, but after nearly a year of war the US and Allies had begun to learn their lessons and internalize hard won experience.

2. Lack of control of the seas. Again Japan's naval forces had to operate relatively far from the good bases of Rabaul or Truk. While the Allies were little better living at the tail end of logistics out of bases like Espiritu Santo. For the USN so long as they could fight the IJN to a draw that was a win. So the gutting of IJN naval aviation in the carrier battles of Eastern Solomons and Santa Cruz that Fall meant that degrading the IJN's ability to support a counter landing was a win for the US.

   And while Japan could make much better headway at night, including multiple successful night surface actions, those could never translate into success on the ground. While night sweeps meant that Allied convoys had to be better protected, and could rarely stay more than a day, and bombarding US positions hurt morale and destroyed aircraft wasnt a sustained presence, as by the time the sun came up those same ships were now at the mercy of US aircraft that hadnt been destroyed and hours from seeing friendly aircraft. So again fighting the IJN to a draw in the night actions, despite painful losses including 3 admirals in 3 months dead, was a strategic win for the USN as it prevented the IJN from being able to cut off the flow of any supplies to the island. And when slow transports arent surviving and you are supporting 10's of thousands of troops with barrels tied together and carried by destroyers your logistics arent a strong point and can be incredibly difficult to stockpile for an offensive, causing delays and allowing the enemy to rest.

3. While there are fundamental doctrinal and cultural choices that did not help the IJA. By using bold, aggressive flanking maneuvers with light infantry the IJA was banking that the enemy could be forced out of their defenses and defeated with the aid of what artillery, armor, and heavy support the extremely limited and prioritized Japanese economy could produce. That works great when the enemy cooperates, there is room to maneuver, and all elements are working together, such as in Malaya, often in China, or the Philippines and Dutch East Asia. But it fell apart for example at the Battle of the Tenaru when a light detachment of first rate IJA troops were landed on the far side of the US perimeter early in the campaign. It was a blood bath as the Marines did not crack, infiltration efforts were unsuccessful, and supporting elements couldnt suppress the Marines defenses, leading to 100's of Japanese troops cut down over essentially open beach and coastal forest in front of entrenched Marines.

Islands of Destiny by Prados

First Team at Guadalcanal by Lundstrom

Neptune's Inferno by Hornfischer

Pacific Crucible by Toll

My main sources for what I'm about to write are John Toland's The Rising Sun and Ian Toll's Pacific Crucible.

One thing that hasn't been noted yet is that prior to Guadalcanal the Japanese had mainly fought second and third-rate opponents. British colonial troops in Malaya were poorly trained and motivated, and Dutch forces in what is now Indonesia were even worse. The Philippine troops that the Japanese defeated were mostly an unimpressive lot as well.

I don't mean to sound jingoistic but US Marines were a very different story. Their junior officers and enlisted men were inexperienced, but their training was tough and some NCOs and more senior officers had combat experience from the USMC's banana wars in the 1920s and 30s. The Japanese leadership had told their men that Americans were soft and cowardly, and they learned the hard way that the Marines wouldn't just break and run the way their opponents had in places like Malaya.

Also, the supply situation for the Japanese troops on Guadalcanal was atrocious. The IJN could bring more men to the island but they couldn't bring enough food to prevent their men from starving, to say nothing of ammo and other supplies. Guadalcanal was supposedly nicknamed "starvation island" by the Japanese. When their soldiers were finally evacuated from there at the beginning of 1943 many of them were walking skeletons. The US supply situation on Guadalcanal was far from ideal, but Marines certainly weren't dying of starvation either.