Q:
the point is ... how is that an exploit as long as the AI can only fire on ONE spot with all outputs?
A:
Anything with piercing capabilities of any kind (so, beams or cannons) benefit from multiple outputs even with focused fire as the beams or cannon rounds will 'fan out' from the point of convergence and hit more blocks than a single large beam or cannon round.
Lock-on missiles all target different places on a ship, so launching many missiles at once can be better than one huge missile especially with massive systems where the radius is capped anyway