The Kalaedinese can give them a run for their money I'm willing to bet, even one of those anti proton beams piercing could deal quite a bit of damage, hopefully knocking down the shields. And the Kalaedinese also use pretty high shield levels.
But yeah, none of the other empires stand a chance, which is fitting I suppose, since the book does mention that their technology is more advanced than the others (minus said Kalaedinese).

Well, looking at the game I ran:

We had three ships per side -
Arcturans - 2 x Hayabusa Destroyers, 1 x Kyouwa Cruiser. A total of 476 points.
Negali - 2 x Yrithar Frigates, 1 x Tabercji Cruiser. A total of 444 points.

The only reason the Arcturans won was that the Negali Cruiser didn't cancel hyperdrive. I think I forgot to tell him that he could cancel it. My bad. Had he not, the situation of the Arcturans:
1 Destroyer gone, 1 stripped of all waepons and shields with just three points of hull left. The cruiser stripped of all heavy weapons, shields and only one point of hull left. The Negali ship? Missing one hull and that was from a forced hyperjump that failed. Of the two Frigates, one jump away safely, the other got kaboomed by a Particle Cannon alpha-strike.

Going with a comparison of capabilities:
Looking at it, balanced. We have the Tabercji vs a Kyouwa and a Hayabusa. The points are slightly in favor of the Arcturans.
We'll assume both ships centerline at range 7.

The Arcturans fire all Particle Cannons. That'll be a total of six. On average, half of them will hit, roughly. That gives six dice for impacts. Against a shield value of five, one impact will make it in, for a rough total of four damage to the Negali Cruiser, with a delay before they can fire those guns again.

Looking at the other side of the fence, the Negali ship: Can risk an all or nothing shot on a 4+. But for sake of math, we'll assume fired separately (Can fire-linked fire independently at the same ship?) Again, one hit, one miss. Here we have three dice for impact, with all dice needing a 3 or better to bump shields thanks to piercing. That's two dice that the odds say will bump through. Now we have eight dice for damage. Granted, dealing with Arcturans, one out of every six shots will be dropped, thanks to Armor Plating. So roughly about seven damage and the Negali can fire again next turn with the same weapon. Now, let's throw in their second set of heavy weapons. (I consider any weapon that can deal more than two damage in a single volley, whether based on ROF, IMP, DMG or traits as a heavy weapon.) Four more shots, half of which will hit, for two chances to bump shields. Half those will make it in, adding another two damage onto the Arcturan vessel.

The Negali ship is hurt, but the Arcturan vessel is nearly crippled. And that was assuming that the Negali ship would have fired upon the Arcturans cruiser. Firing at the destroyer is even worse, as five out of six shots would pierced shields rather than four. On top of that, the Negali vessel will be capable of firing again the following turn, whereas the Arcturan will only have their short ranged weaponry to fire.

Oh and any thoughts of, well the Negali ship has a narrow fire arc with the big guns, I'll remind you that they have overthrusters.

You have to roll one dice for to hit for all Fire-Linked weapons in a single battery that are targetting the same ship. In that case, the cruiser is gutted completely, I'm guessing (haven't looked at the ISS ships for a while)

Apologies if it is bad form to necro this thread, but I can confirm that Negali are more than a match for anything in the ISS.  I've fought them in my last four Starmada battles, losing very badly each time.  In one loss, they scored 10x as many victory points as me playing Imperials/S'ssk.

Negali have decent speed, great shields, and incredible weapons.  If anyone has suggestions on counter designs, I'd be open to hearing them.  I've no idea how to begin, as they seem to have no apparent weakness (I'd say it was long-range, if their Shock Cannons were RNG 15).

I have not-so-fond memories of getting trashed as Dai-Ken against Negali...  Overall I felt that H&C was better balanced than ISS.  The Grumm eviscerators were rough, but they were forward-firing only and they weren't the only thing on their ships...

I kind of like the notion of trait select and then counter-select.  That's what ends up happening in iterated games with no restrictions on shipbuilding anyways...  This just encapsulates it so it occurs in each game, and you have to do less predictive legwork between games because you know more-or-less what they're bringing.  It could be exploited, though, if you choose a central / imbalancing trait as one of your 'counters', even if you're not really bringing it as a counter, and thereby keep it unknown to your opponent.  Kind of an ass move, but...  I'm more for "Here's a bag of random traits, now build a fleet with it" styles of balancing.  The odds of getting a really good combination are much reduced, and you're more likely to see some of the quirkier traits actually fielded.