As one who's job is ship design, the problem is not topweight - it's actually upperdeck space these days. If you want to mount cannon-calibre weapons, you have to be able to site them with R/U locker space close at hand, good arcs (and elevs) of fire and comms to the warfare team. All these areas have to be clear of RAS routes and boat handling areas. Oh and being away from RADHAZ zones also tends to be winner in terms of wanting kids with the right number of heads......
Take a look at the more recent designs and you'll see there is less and less space available with the trend towards "stealthy" designs. Wrong move in my opinion, but don't hold your breath waiting for it to change.