Surely if the Romulans can build a ship that big, the Federation can to?
I would like to think the "size crisis" of the Enterprise is visually-resolved in this one. If we don't see the oversized shuttle bay, it was never there to begin with...
The zoom-in shot of Kirk standing in the bridge window shows the Enterprise is as huge as it was last time. As does the shot of Scotty dangling in the enourmous engineering complex in the first teaser.