AIs certainly do research engines, but they generally have a pre-set or scripted sequence in which they research items.  You did not say what the difficulty or AI level settings were in your games.  Those settings greatly affect how quickly the AI can do research.  Also, the game settings for research costs have great effects on what technology the AIs have at any point in the game.

The attack values and weapon type (railgun) suggest that you and the AIs also were not very far down the weapon research tracks, as was the fact that no ships had any defense.

In the example you described, I personally might simply have researched armor.  Against just 18 attack points, one could quickly and cheaply research a few levels of early armor and prevail.

On general warship design, I tend to build engine-less defenders that remain in orbits and fairly fast ships for offensive and defensive fleet use.  Also, I have found the AI designs generally not worth copying.

Wow, I didnt know about this issue. Is it less ocurring in Dark Avatar? 

Perhaps the developers should fix this in a future patch, if there would every be a new one. The game still sells well, so they should consider some additional effort?

I see more rational behavior in Dark Avatar at the high AI levels.  The AIs will send an unescorted transport at an undefended world, but not at a defended one.  Instead, they will send fleets to beat the orbiting ships first.

Seconded!