What galaxy settings you play at???
Scattered , Loose, Tight??
I play Loose and scattered a lot, it gives me a little more time to detecet enemy fleets, and react accordingly upgrading ships, and buying a last second defense line.
What I meant by that, is that those ships are slow. It would take a lot of small, or tiny ships with engines, to be able to do a blitzkrieg type of atack, since they wouldnt have a lot of weapons onboard. To go far fast you need more than 2 Engines, and that is wasted space on tiny and small ships. For offencive purposes you need medium ships, so the additional space can be used to compensate for the Engines. Of course if you play on tight clustered stars, they will be close so it is more usefull to use the tiny and small ships to atack and then conquer close planets.
However, if you play on loose or scattered like I do, and start playing on Large, Huge or Gigantic, youll notice a diference, and by the time you got enough ships to atack a close neighbor, wich will have more than 6 planets defended with the same amount or close to the amount of ships you are using to atack, prepare to be bitchslaped.
Of course all this can be fixed with Medium Scale Building, so I recomend to at least start researching this tech when you think of atacking some neighbors, cuz if your plan fails, at least you can save yourself.
Just my humble opinion
Monc34