Having the ships fire all their weapons at the same time would go against all Trek precedent. The TOS ship never fired more than two guns at the same time, despite the dialogue specifying plenty of separate weapons. Why call it a bug when it's such a prominent feature?
Failing to fire more than one bank of weapons would make perfect sense if all of the ship's power could be channeled through a single bank. Is there any reason to think it could not? All dialogue treats the total phaser armament of a ship as one integrated entity: if individual emplacements are mentioned at all, it's because they have been knocked out without depriving the ship of overall phaser capacity, or because they are advantageously positioned for firing. Firepower as such never depends on the number of emplacements - it depends on power supply and its possible hiccups.
This doesn't explain why only one ship out of ten in a formation is firing, of course. We could argue that ships share power and channel everything through the lead ship, but dialogue support for the idea is nonexistent. OTOH, dialogue opposition to it is absent, too...
Firing both one phaser and all the bearing torpedo tubes at the same time makes sense, because torpedoes cannot be "channeled". Firing multiple beams at the same target only happens twice: "BoBW" (where two of the three beams come out of nowhere, from places that don't have phaser emitters!) and "Sacrifice of Angels" (where one strip spits out two beams into the enemy).
Timo Saloniemi