Mabe it's just me, but the Thunderbolt stands out already. As a highly-available effective bomber, it is superior to most other fighter platforms on a cost-over-cost basis.
Remember! We don't want to just give races something new that is a no-brainer! We want to give them an option --- not always a good option, either. Something marginal. Something dicey.
The Shadows have to pay in the form of giving up a turn of beam firepower to kill a few fighters --- not usually a great trade. Alpha striking is harder than CAF, forces use of huge squadrons, and you can get shot out of it by having the formation reduced to below pentacon size (I don't think that's enough of a give, mind you). Abbai can't CBD and Regen at the same time, and CBD is the best defensive special action in the game, bar none.
The only other something-for-nothing we have right now is the Shadow Scream, which, given how hard Psi-Corps could sc^&w over the Shadows, is just a rebalance.
The exceptions to the rule are Raiders, Abbai, and Drazi-only fleets. They just need lots of help.
So every good side needs to come with a serious, real, and --- usually --- overriding downside. Not always, just usually.
Trait upgrade don't cost you anything. They're free upgrades. And forcing a carrier to use a special action when it's behind an asteroid field and safe from combat does NOT count as a downside.
If the rule was that it cost a special action and the Carrier had to be within 6" of the fighter (right in the thick of it and next to opposing Primus, Targraths, and Kabroktae ... where a Fleet Carrier isn't supposed to be!). Well, that's something else.
Something .... dubious.
Something cool.
The idea of Sustaining a beam is that, in general, you're going to get far less firepower output. Slow-loading for a 50% firepower output on the primary turn is, in general, a bad trade -- you lose 25% of your firepower over 2 turns. Not being guaranteed its success and not being able to do something else (Come About, CBD, All Hands on Deck) is worse. You'd have to pick your spots. That's, I think, what we're about here.
Dubious options. Where greed, risk, reward, and tough choices make players like me do really dumb things.
Cool.