The Breen attack on Earth never made sense to me. They managed to take out a bridge and scuff up the facade of Starfleet Headquarters.
I like to think their photon torpedo missed or was thrown off the target, but some part of North America is an irradiated crater. The shockwave from a photon torpedo hitting around Alberta knocked down the Golden Gate. The burn marks are from pieces of Canada descending from LEO.
As for the Galaxies firing arcs, I believe it's less that they don't have broad coverage but that their big arrays don't have the reaction time to deal with objects maneuvering so close. However, there are a few actual gaps, directly in front of the saucer section, directly in front of the deflector (where the Odyssey got smashed), and I think (but am not sure) directly behind the engineering hull.