So...
Thunderhawk -> Fighter + Resilient +
full Assault Boat with a +1.
Annihilator -> Fighter + Resilient +
half Bomber with built in turret suppression.
?? That's not even.
What looks like the best option to me is just the same as Ork FBs, resilient save, D6 against battleships. The idea is, Bombers should do more hits against everything except escorts. ABs kill escorts at 66.6% and should remain better at doing that than THAs. Bombers should do more hits against cruisers and battleships where ABs do more critical damage, hindering them. Check the math below...
-4 THs hit a Desolator. 2 THs die. 2 H&Rs against the Desolator, 30.5% change to get 1 hit, 2 H&Rs with no option to roll a 1 and could possibly do more damage with a Fire critical.
-4 original THAs hit a Desolator. 2 THAs die, still 2 hits, possibly chance to get more, 55% change to get 1 hit, 16.6% to get a full critical.
-4 THAs with the FB rule hit a Carnage. 1 THA dies. 6 attacks against it, average 2 hits against it. 30.55% chance at critical.
-4 THs hit a Carnage. 1 TH dies. 3 H&Rs, about 42% chance to get a hit on it, excluding the chance at a fire crit.
-2 THAs with the FB rule hit a Sword. 1 dies, one gets 1 attack against it, killing it at 33.3%.
-2 THs hit a Sword. 1 dies, 1 kills it at 66.6%.
This is the best way to even them out. THAs are FBs + resilient and are exceptionally good at combating enemy battleships and therefore do D6 hits against them. This makes THAs appealing against battleships for raw damage, great at fighting cruisers, and not so great against escorts. THs would be good at hindering battleships, good at hindering cruisers, and excellent (best in the game) against escorts.