I keep hoping to notice a weakness with the plasma weapons but as it is these are by far the best weapons you can put on your cruisers. They do extreme shield and armor damage, they hit from long range, they can’t be countered like missiles can (the other ultra long range weapon), they are a 1 stop shop for destruction. And with a minimum range of 330 and a max range of 900+ there is almost not chance of a ship getting through that window and up close where they hvy plasma’s won’t be able to hit. A cruiser fleet loaded out with these, in my experience, can only be countered by another fleet using the same tactic. They just annihilate everything. (give them a minimal escort of fighters and some escort frigates) They do miss occasionally but when you have 15 of them firing, as long as 50% hit, the target is done for.
Some possible solutions:
Take away the shield or armor penetration. (It should get one or the other) I think a short range weapon could have both types of penetration without being unbalanced but on a long range weapon it gives you and easy kill while the enemy isn’t in range.
Assuming you took away it’s shield penetration the weapon might serve very little purpose as a ranged weapon that can’t get through shields won’t help much prior to the enemy getting close. Plus there isnt’ much that can take down shields at their highest resistance so without this weapon shields might become even more powerful. (If you haven’t tried trippling up on the highest resistance shield you are in for a treat)
Assuming you took away armor penetration this weapon could be useful to weaken shields but wouldn’t be a kill weapon from long range, just a harassment or support weapon for heavily armored shorter range ships.
I think I’d vote for taking away armor penetration, most of the other stats would work fine if the Plasma was a dedicated anti shield weapon. And it would be more in line with the long range missle weapons which seem to harass more than they kill.