After the destruction of the D it was decided that families would not be on board starships, especially children as it is just too dangerous in which case the design no longer needed to cater for them hence the more streamlined Sovereign, designed by Montgomery Scott I do believe who knew better than to have ready made hostages on a Starship.
Its also a more powerful ship overall, they carried on building Galaxy class ships but they were not to be sent into such danger again, they will send the Sovereign class instead.
The development of the Sovereign is a bit of an about face from the exploration/diplomacy designed Galaxy class to a more effective warship, Starfleet didnt want to get caught with their trousers down again.
For me the F looked like a return to the exploration and diplomacy aspects as its a very large ship with a volume approaching twice that of the D, but it isnt canon unless they make it so and after the destruction of Romulus and the attack on Mars I doubt we will see anything like it as Starfleet seems to be in a warship type mood.