Drake-class Missileship: This one's borderline. In the early game they're reasonably threatening, making them closer to minibosses. Still, given that they can show up as early as the second system of vanilla or the first system of Eternity Port, they probably shouldn't be quite so hard to take down with low level weapons. I'd recommend reducing the compartment health a bit.
Tripoli-class Destroyer: I've had fights against these where they were literally unable to scratch my armor. That was probably with level 9 armor, which won't always be available when the player is facing these. But by the time they show up, there's a very good chance the player has access to level 8 Carbide Carapace, which renders their lasers ineffective and their missiles very weak (except for the 10% chance of KM550 Broadswords). I suggest replacing the KM110 Starbursts with KM120 Brutes and the turbolasers with a particle weapon of some sort (something that falls in between the Particle Beam Weapon and the Tev-9 would be good, but I'm not sure there is such a thing in vanilla). Also, they have almost as much compartment health as Deimos-class Destroyers or Ranx Dreadnoughts, so that could be reduced a bit.
Ranx Dreadnought: For all their intimidating size (bigger than a Phobos!) and flashy weapon graphics, these guys are hilariously ineffectual. Part of that may be due to this bug. But even if all the fragments were working, the Kiloton Cannon seems rather weak for the main gun of an enemy that ought to be a late-game threat. (6.5 thermo damage times about 3 hits) By comparison, a Gotha-10 missile has 1/3 the mass and does 100 thermo damage. I recommend improving the Kiloton Cannon's damage substantially (and maybe raising it to level 8).
Edit: I may have underestimated the average number of hits, as well as the value of doing some damage with shots that would miss if they didn't fragment. But I still think the Ranx dreadnought needs more offense, so either the Kiloton cannon should be raised to level 8 and buffed accordingly, or the dreadnought needs a much better fireRateAdj value.
Sotho-class Gunship: These are a bit too big and tough to feel like cannon fodder, but their weapon is too weak to be threatening.