The problem was that they were constrained in the amount of fuel they could get to the fleet at any one time. They didn’t have a pipeline and they were constrained to their tankers. This meant that for any given volume of fuel, they could have run the Yamato by itself on one mission - or run the entire rest of the fleet on more than one mission. Bang for the buck wasn’t there with the Yamato, and that was the fuel problem. They couldn’t get enough fuel to the front fast enough to get the Yamato to run on regular missions as well as the rest of the fleet.
Musashi didn’t get her AA armament upgrade until late in the war as well, and her end was also late enough in the war that US forces had more than rebounded from Pearl Harbor (1944), so yes, by that point it was irrelevant - but during the Guadalcanal campaign, it would have been critical as at that point we didn’t have the forces in the area to simply throw at an objective until it went away, as we could later in the war.
The Japanese had thought the war was going to be one of battleship duels and had concentrated all of their 18” shell production on AP, star, marker, etc., etc., and had pretty much ignored HE and frag. They had a huge mountain of shells for the Yamato and Musashi... of the completely wrong kind to actually do anything effective for shore bombardment. Even the secondary armament didn’t have much useful and they were not dual-purpose guns.
Also, the Japanese ‘advantages’ at night fighting consisted largely of the fact that their torpedoes worked and ours didn’t. The other advantage was that the US radar at that time was basically useless close in against cluttered island chains and such and therefore was negated - and the Japanese had superior optical rangefinders.
“They couldn’t get enough fuel to the front fast enough to get the Yamato to run on regular missions as well as the rest of the fleet.”
Not quite true...
The Japanese solved this problem for most of the war by stationing the battlewagons at Brunei, close to both the oil, and the refineries.
It was only after the fall of the Phillipines that this became untenable, and the surving big ships returned to Japan.
Also, Yamato was heavily damaged in 1943 by a torpedo hit that almost sunk it. It made her captain and crew aware of how important Damage Control was to modern fighting, and they trained heavily for it, one of the few IJN ships to take it seriously.