Fisher’s Dreams and Tedious Realities
What was needed was a ship that used only cruiser-type resources, plus whatever odds and ends could be scraped up from the remains of the 1914 battleship programme. Steel plates and framing were easy; more could be ordered for ‘cruisers’, and a deeper hull with thicker layers of top and bottom plating could take care of the stresses experienced by a large ship. Machinery wasn't difficult either, as sets were now on order for ‘C-class’ cruisers. As in Glorious, this machinery could be grouped to produce the higher powers needed by a larger ship.
Neither of these schemes appealed greatly to Fisher (although the design for the four-turret ship would later be developed in other ways), as they would take long to build and wouldn’t produce anything that was significantly better than Renown.
He was on the verge of accepting a modified Glorious instead, as that could be built quickly, when the Engineer-in-Chief came up with a new way of combining turbine power, and Armstrong’s works came back to him with a proposal for a new 15” Mk.2 gun.
I feel like we're just ignoring wartime constraints here and you aren't portraying Fisher anywhere near correctly. You can't just run by and swipe up all of the machinery (boilers or turbines) for cruisers when historically the Chancellor of the Exchequer had forbidden any larger ships than light cruisers for this exact point. The RN needs cruisers quite badly in this stage of the war and is attempting to pump them out as fast as humanly possible. Even for Fisher, diverting these very expensive and limited resources away is not very plausible. You can't just magic up new boilers and especially turbines, they are bottleneck items with a long wait time for replacement. We're getting too far into capital ship building wank while forgetting the very realistic constraints placed on Britain during wartime conditions. Also I dearly hope we aren't going towards triple or three gun turrets because the British also completely loathed them as well. Sticking with another 15" gun even an improved version is not with Fishers MO whatsoever.
Fisher is being a little sneakier in the story, and he's already used up more turrets on the Renowns, so there is less of a choice.
Perhaps the Follies are not seen as the magnificently high-quality product they were in real life . All will become clear in due course...
I think British dislike of the guns was more along the lines of "not invented here" than anything else. I have no doubt they were 'export grade' - i.e. not quite as good as one might build for oneself. On average, US guns seem to have been less accurate than the British ones (right up to the 2nd WW), however it is possible to argue that a slightly spread pattern gave a better chance of scoring a hit in pre-radar days, so that isn't necessarily a flaw in any American designs.
Roberts, Raglan etc.. gave reasonably good service once the bugs were worked out (and don't you wish they'd stuck with the original names, however politically inappropriate they were - even by 1915 standards).
The British didn't like the guns because they didn't think they were of sufficient quality to meet Admiralty standards, especially to the point where they would be green lit to be placed in new Royal Navy constructions. Lower quality ships with lower quality guns were used by the RN during the war but these were basically exclusively whole sale foreign builds that the RN took over, they didn't take off their weapons to slap them into new RN builds for a very damn good reason. Fisher would be very unlikely to want 14" guns (a clear step down from the 15" gun, same with the Admiralty at this point). Fisher would have rather waited a few years for a new gun such as the 18"/40 gun (which he historically did) or the monster 20"/40 (as he also historically did in 1915, which was confirmed in d’Eyncourt’s papers as being design finalized at this time)