The general point was that the WNT in the OTL and this scenario, is focussed on the idea, that no state wanted to get involved in yet another arms race, which eventually had sped up the Great War to begin with. Shortly after the War, the Allies, especially teh UK and France, but also the USA and to a lesser sence the Japanese Empire, wanted to ease down armaments and especially the cost of it, given the more urgent domestic needs.
Althought the UK were in a poor economical situation, shortly after the war, it still had all its resources and manpower in its empire, besides its infraastructure to continue a large scale naval building program. The infrastructure was dramatically scaled down, following the WNT signings, but was still intact in the period prior to 1925. In theory, the UK could easily have produced new large warships at the same speed as before the Great War, although the budget would not have allowed so.
The USA also could produce quite a lot of equipment, if needed. Economy was not yet the problem here, but the enormeous size of the program would eventually leed to problem, sicne most economic power was already on loan and credit, eventually resulting in its collapse in the late twenties. The large program would have aided to speed this proces, propably with worse results domestically, as it would also overlap with the same period of the Roaring Twenties. The US politicians were qute happy, the buildingholliday was called, so more attention could be turned into the own economy and domestic issues.
Japan was actually not at all happy with the WNT in the OTL and would neither have been in the Scenario, as it was not getting its wanted large pwoer status, being limmited to a more regional power only. It wanted to be able to dominate Asia, without interverence of other large powers, especialy the UK and USA. For this it wanted to have more or less parity with the other large powers, including the UK, which remained the strongest, given the knowledge the UK and USA could neither deploy their whole fleet against the Japanese, given their other reponsibilities in the Atlantic. Dispite Japa'n's much weaker economy at this period, it seems not impossible to get at least the reduced variant of the 8-8-8 program would eventually be completed, as in the OTL Japan still continued to produce quite a large number of expensive navalunits in a short period of time. (The development and buildingcoast of the new Heavy Cruisers of 10,000 tons official was about equal to building a larger, more conservative battleship. Japan produced 8 Takao's and Atago's in the late twenties, besides quite a large number of other navalships, including the first large superdestroyers, which were also quite expensive.)
In the OTL the USN may have had a large fleet, only slightly lesser in numbers than the Royal Navy, but considerably larger than the Japanese. It was however somewhat illballanced, having almost no cruisers until the 30's and a very old design of destroyers to support the fleet, hardly capable of performing in its inteded role, due to lack of range and capabilities. Only its two large Carriers were superior in layout and number of aircraft, which became valuable in the next war.
The Royal Navy was left with a large number of old and worn out ships, all with lots of heavy warservice of heavy steaming. The 15 inch gunned ships were good, but needed refits to make them usefull in the modern period. Its excelent support force was a bit onesided at first, being focussed on the North Sea only, but the UK quickly started to construct new cruisers for its colonial and Imperial tasks (County Type). The Royal Navy also had a very large number of destroyers, of whom the V&W types were exelent and modern enough to continue in the postwar fleet, while a few older and smaller ones were retained for otehr services. New additions continued to be added, of the A-I types, who all were much better than anything the USN had at the time and most of the IJN, except the Special Type.
Japan was also producing and upgrading its fleet constantly, with interesting and powerfull designs. On the whole a quite ballanced strikefleet was created, only weak in the secondary considered ASW. For some reason, the economy did not suffer that much, as some might expect, although the lack of industrial production limmited the production of essential materials. This may also have happened, when Japan continued to construct the 8-8 plan, in stead of the new heavy cruisers, who essentially replaced them on the buildersyards. For the 8 heavy cruisers of the Takao and Atago class, Japan needed only to have completed just the already being constructed Kaga's and Amagi's, plus four additional battleships not yet laid down. The four Amagi's and both Kaga's were quite well advanced, when the WNT ordered them to be canceled. Money already was expended before thism, so only four more ships needed to be funded, rather than the 8 ships of the new, post WNT cruiser program. (Amagi was lost during the 1923 Tokio earthquake, so a fifth ship might be added, after the this.)