I noticed already in Beta that having 4 front mounted cannons can be rapid fired infinitely without energy dropping at all. Try that with Beams... urks.
TL;DR version: Why do more than 2 beams suck so incredibly much energy. They are already the lowest dps weapons and I wonder how the later cruisers will be able to sustain their 4/4 gun slots if more than 4 beams already manage to suck weapon power down to zero in zero time. One wonders why not at least the huge cruisers are able to support their beam arrays with enough jouce.