Sorry i cant help. Tried to connect. The game apparantly only singleplayer

Let's take a fleet of tiny fighters each dealing 2 damage.
you attack, so you make 10+9+8+7+6+5+4+3+2+1 = 55 damage if all your ships would be destroyed.
The addition comes because every turn the dreads are killing one of your ships. I took 1 damge instead of 2, because sometimes you deal 2 and sometimes 0 in the middle you should make more then 1, so calculating with 1 damage will be certain.
As you see you make about 55 damage until all your ships are gone, all dreadlords I saw had below 50 hulls. Tiny ships are cheap and they are produced fast, when equipped with more guns you'll need less ships.

In that particular mission, you might be better off avoiding fighting the DL altogether. First, send colony ships to get what planets you can- your priority is to get one as close to the Drengin world as possible. Then, research Planetary Invasion (100% to research). Then quickly build up a fleet of high speed, long range fighters and transports. Zoom into Drengin space and take the planet before the DLs have really got themselves going. You don't even have to fight the Drengin ships (make sure you're fast enough to avoid them- all you've got to do is take out the ones orbiting the planet).

That said, you can't get away with that later on in the campaign. In those cases, tiny fighters are one possible tactic. Another important thing is to make sure you get first strike, sometimes you can destroy the enemy before they get a shot off. Military starbases can also really turn it around. Also, taking DL planets can give you some very, very good tech.

well one of the things about the campaign is that you can lose a mission you won't get a gameover screen. You can simply play an alt mission.