Adding bigger ships to the federation that trade maneuverability for more firepower and survivability is a response to the factors that currently make space PvP boring - namely having to huddle into a pile waiting to be attacked or squaring off against carriers that have practically no weak spots.
Instead of asking for a ship that plays into the factors that make space PvP sucky and boring in the first place it would be much more sensible to ask for things that make space PvP more fun in the first place.
Also adding larger ships just blows away the frame of reference. cruisers are already absolutely massive, they just don't seem impressive because you're comparing them with Negh'vars and Carriers. If you really want to have a sense of scale for your ship you should ask for more small ships that are worthwhile using, not for even bigger ships.
Lastly, capital ships erode the playstyle for a faction. You see Klingons go into PvP with nothing but carriers, if Federation had one you'd see Federation go in with nothing but carriers. What then? Carrier wars? The real focus should be on making the existing ships cooler, fixing abilities so it isn't all about RSP and FBP, thinking about more ways to make a ships speed into a meaningful factor in combat etc.
As i said in the carrier thread "Carrier Trek, Boldy going where Star Wars has gone before"