A Plasma Cannon shoots three bolts at 700 range for 750 damage each, totaling a burst of 2250 damage, with 652.5 DPS and 900 flux/second, and uses up 30 OP.
A Joyeuse Fractal Laser shoots six bolts, which can randomly split into more bolts (at most ranges at least eight will hit the target) at 1200 range for 700 damage each, totaling a burst of at least 4200 damage, with 600 DPS and 857.1 flux/second, and uses up 40 OP.
You're buying vastly superior range and burst damage, plus the ability to power through usual obstructions like fighters, missiles, and asteroids, and also get through shields without wasting all the damage on an overload (since only one or two bolts will hit while the others pass through to the hull), for very slightly lower DPS and an extra 10 OP. I don't see a reason to buff it.
A Merced Cannon shoots 60-damage bolts at 550 range, with 300 DPS and 375 flux/second, and uses up 10 OP.
An IR Pulse Laser shoots 35-damage bolts at 500 range, with 105 DPS and 150 flux/second, and uses up 6 OP.
A Pulse Laser shoots 75-damage bolts at 600 range, with 225 DPS and 330 flux/second, and uses up 10 OP.
You have a point with how much of a monster this weapon can be. I don't think increasing the flux cost is the answer; rather, I'll be decreasing its range to 500 and lowering its damage to 50 per bolt, bringing it to 250 DPS. Then, compared to a Pulse Laser, it has slightly better damage at the cost of worse range, armor penetration, and flux efficiency.
A Rhon Laser operates at a range of 500 to deal 300 DPS, costing 450 flux/second, and using up 12 OP.
A Tactical Laser operates at a range of 600 to deal 75 DPS, costing 75 flux/second, and using up 5 OP.
A Phase Beam operates at a range of 700 to deal 175 DPS (150 DPS in vanilla) and 20 EPS, costing 160 flux/second, and using up 12 OP.
A High Intensity Laser operates at a range of 1250 to deal 300 DPS (250 DPS in vanilla), costing 250 flux/second, and using up 20 OP.
Compared to vanilla beams, the Rhon Laser is in an entirely different world. It has no charge up/down time either, making it more efficient than either of those other beams in any situation that doesn't require continuous fire. Compared to a Phase Beam, its only disadvantages are a shorter range and a large efficiency penalty; this is a small price for being a slot smaller and nearly twice as powerful. The Rhon Laser isn't designed to be a primary assault weapon; it's an unstoppable point defense beam. I guarantee no fighter will last against these things. Slap an IPDAI on the ship and you have the best small-slot point defense weapon in the game.