So, we build a 1 mile ship to counter a 5 mile ship. Why not build a ship of exactly that length, or maybe double the size, to counter this ship? That didn't work for the Imperial Navy, as one fighter took out the bridge and brought the ship crashing into the Death Star. Imagine that happening in Star Trek.
An enemy ship smashes into your bridge, and, considering, that you left the bridge far more vulnerable to attack, as you idiotically put in openings on either side of the bridge structure, there goes your expensive penis waving project.
None of these designs seem all that smart from the military built-to-protect perspective. But if you want another way to take out the big saucer with the hole in the middle, take a page from one of the Shatner/Reeves-Stevens novels, where they have a DEFIANT-class Enterprise decloak INSIDE the open area on a TNG-era Warbird and just fire while rotating around inside that empty space between main hull and engines.