I think your observations are spot on. Navies build ships to meet their specific needs. The RN has lots of water to cover, and the advantage of many bases, so they need, and can support lots of smaller ships. That's also how they can use guns with short barrel lives, they have many bases to replace them in. The USN for example needed to operate far from home bases, but this is something everyone here already knows. Let me make another point about the efficacy of building armored cruisers.
From pre WWI to WWII naval guns, and shells improved, and the range of combat greatly increased due to more advanced fire direction. It became harder, and harder to design a ship with enough armored protection to resist a similar caliber shell that they themselves carried. Greater range made this even harder because plunging fire made more deck armor necessary. That's why it was easier to design a reasonable armored CL on a 10,000 ton hull, then a CA. No one had prewar CA's that could resist 8" shells. The USN Baltimore Class, post treaty CA's were 4,000 tons over the preceding Treaty USS Wichita. An armored, or super cruiser with 9.2" guns would be nearly 20,000 tons. How many ships of that size would any interwar navy build?
Not even the Americans would build them, just where would they fit in their naval doctrine. The reason the USN built the "Large Cruiser" Alaska Class, (Over 30,000 tons,) was faulty intelligence, that the Japanese were building super cruisers. Interesting that U.S. Naval intelligence underestimated the size of the Yamato's. If they'd know they would've completed the last 2 Iowa's, and given the Montana's a higher priority. Really would have been a waste of resources, more Essex Class Carriers would've been more useful.
Along those lines what about a TL with no WNT where the USN converted all 6 Lexington's into carriers? That would be a real Black Shoe vs Brown Shoe battle. What would an international Carrier race look like? How many could the RN build, or convert? Would the RN take back the Fleet Air Arm? How would the Japanese respond. The French converted an old Battleship into a Carrier, in the late 30s loaded out with American Vindicator Dive Bombers, a plane that was unfairly maligned. It did good service as a land based DB, during the Battle of France. Everyone had large ships suitable for conversion, including Liners. During WWII Italy was converting 2 liners, but didn't finish them in time. This TL would certainly see an acceleration in the development of naval aviation. Any thoughts?
Totally - and we are talking - what 3 Deutschland class Armored Cruisers - which were no more armored than any heavy Cruiser - they were vulnerable to 6" shells (which mission killed the Graf Spree) and a single 8" shell hit effectively crippled the Graf Spree
So had the worlds navy's started spamming out CAs or lots of Heavy Cruisers then at extremis I can see the Towns being built as 8" gunned ships
As for the Carrier race - I always saw the carrier laid down in the 20s as experimental (granted they muddled through) - it was not until all of the learnings aligned with the Ark Royal that we saw the start of proper purpose built fleet carriers - with the ultimate expression being the Shōkaku-class and Essex class.
For Britain I could see them pretty much doing the same thing - make the RAF the 'owners' of air power during the 20s and 30s (the principle perceived threat to Britain was Bombers from continental Europe) but with increased carrier aviation the FAA would have a greater say in aircraft development and be more likely to achieve 'independence' earlier than OTL.
Carrier construction would be close to OTL I think with the Outrageous class being converted as well as Hermes Eagle and Argos - all pretty much grasping around learning the ropes of Naval Aviation.
But with more carriers in other navies (particularly if the US builds 6 Lexington CVs) I can see more and earlier purpose built CVs - an earlier 'lesser' Ark Royal
And with more follow on ships from that design into the 30s - with either an expansion into that type of ship or like OTL if the threat is deemed as a Littoral one then a move to Armored carriers