The complaint was a valid one. The US continued to equip infantrymen with the Springfield M1903 rifle bolt action rifle. Which as the name might suggest was first produced in 1903. Most of the units were using the M1903A3, which were produced in the 1940s. So they weren't using 40 year old rifles, just a new variant of a 40 year old design.

The US had selected and was producing a replacement in the M1 Garand. The M1 was a semi-automatic rifle capable of much more rapid fire. And the US army started swapping out M1903's in the 1930s. There was nothing wrong with the M1903. It was for the most part a solid weapon. But as a bolt-action it was comparatively slow. Each trigger pull had to be followed with a cycling of the bolt, to eject the expended casing and load the next round. The M1 only required a trigger pull.

This procurement replacement wasn't complete by the start of the war, and the need for more rifles as the army and marines rapidly expanded. This meant the US began buying up everything they could get their hands on. Springfield cranked up production of the old rifle. Even Smith-Corona (the typewriter company) got in on the war procurement game producing the M1903 under license.

The marines frequently got second tier material, and the European theater was given priority over the Pacific. So the early M1s tended to go to units heading to Europe. So yes marines were thus often using the M1903s, especially in the early months. As the war progressed, the M1 became more ubiquitous and replaced most of the M1903s. But the older guns were never entirely phased out as a primary infantry weapon until after the war.

Even then the M1903 got new life as a sniper rifle, where speed wasn't a significant issue. It was in use as late as Vietnam in that role. So it's just possible that there was a marine on Guadalcanal who was using the same model of gun his grandfather used and that his grandson would use. The gun was used by 4-5 generations of US infantrymen.

Something worth mentioning is that old isn't necessarily synonymous with obsolete. The current standard issue rifle of the US army and USMC is based off a design from the 60's. The AK-47 celebrates its 70th birthday next year. The M1911 and M2 are both still in active service, despite being over a century old. Just because a design is old doesn't mean that it's not the best option.

Indeed, sometimes new technology is actually less effective than that which already exists. Much has been made of the alleged technological superiority of the Indians over Custer at the Battle of Little Big Horn due to the 7th Cav being armed with single shot breech loading rifles rather than lever action rifles. But studies after the conflict found that breech loaders actually have a higher rate of fire in the long run.

The TLDR of it is if it ain't broke, don't fix it. And the old bolt-action rifles that the USMC were armed with were still perfectly functional in their intended role

Browning 30 cal machine guns - manned by two - also came late; the Vickers was accurate and reliable but it required four men and a healthy supply of water to operate.