A lot of the bombers received shield regeneration buffs. Retail doesn't support that flag so all ships regenerate the default 2% of their maximum shield energy per second, the bombers in BPC have all been buffed to 4%. This means they regenerate their shields in 25 seconds instead of 50 seconds, assuming max shield ETS. With "standard" ETS it's 75 seconds instead of 150, which is still pretty relevant.
Some bombers have also received big weapon energy buffs, since in FS2 retail bombers weirdly have the lowest weapon energy. A Perseus has 150 while a Boanerges only has 100. The Artemis was buffed from 100 to 170, an increase big enough to let it sustain fire from it's quad-bank.
Many other bombers have been changed from 100 to 130-150, depending on their weapon configuration. The Artemis also got actual engine OCLK speed, in retail it's always limited to 65 no matter how much ETS you put on engines, BP changed that to 78.
The Boanerges specifically also got slightly buffed turn times(from 5.5, 6.0, 6.0 to 5.0, 5.5, 5.0) and a decent AB buff from 85 top speed to 100, giving it more unique advantages over the slower Ursa to compensate for not having a turret.
On the fighter side of things the Myrmidon changes have already been mentioned, the Erinyes got a suite of buffs to make it suck a bit less, a very light rotation time buff(from 3.8, 4.2, 3.8 to 3.8, 4.0, 3.8), reactor buff(shields from 500 to 620, weapon energy from 150 to 200 along with weapon regen going from 4% to 5%), very slight health buff (from 325 to 350), and a slight nerf to afterburner duration though the speed and recharge stayed the same(AB fuel from 420 to 350).
The Ares also got a weapon energy buff from 180 to 230, remaining the highest in the game, and the Herc II was buffed from 150 to 165, a rather small increase that doesn't matter that much considering the 2+2 layout generally isn't very power hungry.
As for the Myrmidon being a good all-rounder... no, not really. The Perseus with Trebs does it way better. The Myrmidon is bad at dogfighting due to its huge target profile and lethargic turn times, weapon compatibility doesn't fix that core problem. Its speed means it can be used as a decent strike bomber but definitely not an all-rounder.