but if you look at systems aboard both Oberth and Mirindia class's there systems match a Consistion refit. So a Connie would have the excact same system layout, and we do not know when the isolieaner computer came out so you could speculate they still use duotronics though refined still in the new excelscior, though in 2294 aboard the EnterpriseB we see what looks like an early isolineaer computer, so excelscior could have been the test bed it did use alot of new technology, also if Mirandia was set to replace the Consistition then what purpose was there to bring the Excelscrior fleet online period. Not only that but Mirandia's lack the room for the science labs and weapons systems of a consitition class, so it couldnt have been the replacement heavy crusiser, nor could have constellation which seems built purley for combat, with 4 naccells and 4 forward firing tubes each capable for 2 shots giving a total of 8 photons per volley forward, Constellation seems more like a ship built for war, which doesnt make sense, as the ship was still undergoing trials when the Kitomer Accords happened, so why would Starfleet keep the ship operational afterwards.
Also it has been theorized that the Enterprise A was a newly built consitition not a refit yorkshire as Star Trek IV puts the Yorkshire adrift in deep space, and unlikly to the new ship. So why would a brand new Heavy Cruiser be scrapped just 7 years later? Remember it was set to be scrapped before they knew of the Kitomer Accords, so Starfleet was phasing out the entire fleet, but it makes no sense to build a new one to phase it out 7 years later.
Also arguing the class was old, the Excelscrior class was launched in 2285 and served upto 2380 we know, thats 95 years, Miridina class's we saw as easly as 2285 but given Reliant's status and the mission ect you can speculate the class was introduced in the late 2270's at the latest, putting that class at 100 years or older and still in fleet duties. OBerth no clue but at least 100 years given we saw Grissiom meaning Oberth was launched earlier than that. But the Consitition was scrapped after 53 years, it doesnt make sense for Starfleet to do that given there use of other ships for far longer. USS Hattaway was commisioned in 2285 according to her plaque though the Constelation was still undergoing cirtifications in 2293 but that puts that class also at 90 years in service, as last time we saw them was in DS9, so 2375, it doesnt fit to retire the consitition or it doesnt fit to keep these 23rd century ships working into the late 24th, you decide.
As for the argument just the A was retired, it was 7 years out of refit or construction no one was very clear on this ever from Star Trek we get two seperate histroyies one was she is Yorktown and one she was an a ship awaiting commission, but either way if they retire a ship that was refit and from what we can tell in STV almost totally rebuilt again with massive systems upgrades given the Warp Cores and decks dont match the Original Enterprise, refit it would have been another extensive enteral refit so why retire it?