In DS9 the K'T'Inga fired a disruptor from the torpedo recess, not an ion cannon. That is the remit of games, not canon Star Trek.
In the DS9 episode itself, CC22, the beam coming from the photon tube is red. Bright, deep, red. Klingon (and Romulan) disruptors are green. in DS9, Federation phasers and photons are yellow-orange (though that may just have been your crappy quality NTSC TV instead of the superior PAL
). In STII, Federation phasers are orange-red.
Ergo, the K't'ingas are not firing disruptors or standard phasers. I'll grant that maybe the finally developed those Klingon Heavy phasers, though. My saying it is an ion cannon is indeed fanon speculation, but disrupters they ain't.
Don, the SFB K-D7 is a superb attack ship. Massive and varied weaponry suite, of phasers, heavy disruptors, and drones. That these ships only have Ph2s is a range limit only. Klingons like to get in close, and up close the Ph2s have only slightly less power. Plus, the Ph2s are listed as offensive/defensive phasers. They can take out drones at greater ranges, or be used to come up close and shatter your shield because the Klink has so many of them. The Federation's Ph1s (in early, at least) only gives them a range advantage. Besides, I'd rather have the D7.
7x Ph2s (covering ALL arcs and allowing at a broadside of 5 from almost any angle), 4x Disr 3s, 2xDrn As.
Put that against the SFB F-CA.
6x Ph1 (allowing a broadside of 2, but the rear arcs are blocked at critical angles giving NO coverage), 2x Phot.
Add into that the far better manoeuverabiliy of the D7 and the F-CA's shield and hull advantage is neatly countered, and quite often superseded. In the Early era (no refits) the Federation has a range and endurance advantage. The Klingons have a "weight of firepower" and manoeuvreability advantage. Each side tries to play to their own strengths and get the enemy to the disadvantage.
This, my friends, is the main reason SFC1/2/OP is far better than SFC3. In SFC3, everyone is armed the same, with a the Feds at a cloaking disadvantage. In the Pre-3 games, different strengths and weaknesses meant it was about skill, strategy & tactics. Different strengths and weaknesses meant you had to fly differently for each race. I got rid of SFC3 after completing the single-player campaign and a few frustrating online games.
Pre-3 Rules!