Can someone explain the weapon power limit?

The big ships have higher weapon power limit and two cannons, but they always seem to deal less damage. How do they work? Do they scale better later with more firepower than the single cannon ships?

The power for bombers is being shared between both weapon pylons. So, for example, if you are at 3 :zap:, then one of your pylons is 2 :zap: but another is still 1 :zap:. This results in bombers being more powerful closer to the outer range of their firepower limit.