One of the core Interstellar Shitshows of the first half of the 2260s in EoM will be the collapse of the Kingdom of Acamar into a long civil war, which serves as the last big foreign policy incident before the Organian War/Romulan Incursion in 2267
As we know, Bob, the Acamarians are a spacefaring civilisation based on Clans, who, in the late 2260s saw a large amount of their population leave to become "the gatherers" instead of settling down
So In EoM, the Acamarian Kingdom has just managed to bring it's long clans wars to an end in around 2260. While it is surrounded by Federation Territory, it is still not a Federation member.
Having Watched WoK last night I think I've figured out the reason the Miranda class is so long lived: it's not a "light" constitution class - it's a "pocket" Connie : same firepower, defences and speed in a small, more compact, less temperamental spaceframe
I suspect when the Constitution was redesigned at the end of the 2260s, the Miranda class was able to take advantage of all the upgrades in a much more radical fashion - in fact, pre 2270s "Miranda's" as seen in the Early voyages comic,might not even be the same spaceframe at all
These two (the USS Cortez and USS Achilles) seem less like Miranda's than a light refit of a Connie Saucer Section (which is probably the least complicated part of the Connie, which is why it's seen in the Miranda, Saladin, Larson etc.)