one thing to keep in mind is the excelsior and the conny have a very differnt USEAGE.
the Conny was retired and relegated to history. the Excelsior class meanwhile seems to just be the gift that kept on giveing, serveing as the primary cruiser of starfleet well into the TNG period, I suspect the excelsior just was a perfect storm of things that allowed it to continue in service, for longer then it's predecessors and even attempted sucessors (the Constellation was proably a post excelsior design, yet there's evidance the excelsior si contineuing in service while the constellatiion was an ageing relic slowly being phased out) my guess is the excelsior mated a highly reliabler, dureable and roomy hulll thus allowing easy upgrades, as well as extremely reliable basic systems.
in short the excelsior is the B-52 of starships.
All of that is dated. In the book, and the timeline, they point out that starships in the current STO modern starfleet are subject to their modular design advancement in technology. Which means that NX you see and that Connie you see aren't actual NXs and Constitutions class ships. They are modern ships modularly designed to LOOK like the classics. Just like that excelsior. Every ship in STO is a current ship. Because the timeline takes place in the future, a good chunk of time in the future.
So the whole argument is just sort of silly at this point. None of you are flying a B-52. You're flying a modern starship that looks like an older one.