Well naturally the Mimbari who are vastly more advanced would have better
Thats a duh. Though, the starfury was a huge bain for Membari Fighter Aces. I can't quote you the book but "If" I remember correct. The Membari enjoyed a kill ratio or 15 or sometimes even 20 to 1 against people they fought. During the Earth-Membari War, that rate dropped to 8 to 1. The Membari suffered greater losses to EA fighters then they did from EA capital ships. Again, take this with a grain of salt as the early novels weren't canon and some were fully over ruled by the later B5 movies. What this does do is give a somewhat fair view of the ability of the EA fighters and pilots against the best aces in the known galaxy.
It basicly made the EA a superpower.
I agreed totally with this. It seems a fair reason as to why every new ship design from the EA after the Earth Membari War were built as carriers along with their normal combat ideals. Just take a look at the number of fighters the standard EA ship carried vs every other race. The Omega, Marathon, Warlock and Nova all carried 36 fighters. Most other races only carried around a dozen or so.
Thunderbolt was capable of atmosferic flight, did that in any way effect its space performence?
It suffered slightly in space from the added weight. Though it had a far far greater rate of fire and better armor. Plus being able to move in and out of atmo is a great advantage in battle where most of your enemies can't.
It was weaker than the Mimbari fighter, but we never got any real conperecment to the Narn or Centauri fighter. So was it realy better?
Well, the Narn built their fighters around attacking capital ships. This was to make up for their lack of heavy warships againt the Centari Republic. As for the Centauri. We did see them against starfury squadrons. A Centauri Primus attacked B5 and the fighters from both sides met in the middle. The CR fighters seemed to be pretty fast at first but the fighters had been wipped out within a minute of combat. Even though they were out numbered 2-1, it should have taken a lot longer for the starfuries to do the job. That leads me to think that the CR uses its fighters as only an after thought in their battle plans. Both their ships and pilots were not even close to being a match next to those in use by the EA.
The weapon was impresive. A bunch of them were capable of taking down a Centauri Vorchan and dealing great damage to a Primus.
Their payload was insane for a ship of its size, I'm speaking about the standard starfury. They had two weapon systems that I knew of. A pair of side mounted twin light cannon for anti fighter fire (high rate of fire but low damage) and a pair of heavy cannon underside for targeting capital ships (low rate of fire but high damage). The later thunderbolts had the big chain gun (high damage and high rate of fire) plus they had hard mounts for missiles and bombs.