What we saw was a Miranda class starship being involved in a Top Secret operation, while The Enterprise was relegated to being a training ship.
I mean, if you really start to look at things, by the 2280's the Constitution was definitely not much of a "Front line Starship".
There had to be something between the Constitution and the Excelsior that was meant to "awe and inspire".
Yeah it would make sense...but as we apparently have decided...No Screen, No Canon
I would imagine the Shangri-La-class fills that Constitution-Excelsior gap now as a sort of turbo-charged beefed-up Constitution-class, possibly with some elements of Excelsior engine/power tech going by the shape of that secondary hull and oversized impulse engines... and it's canon because we saw a model of one in the Titan-A's observation lounge. Sigh.
