That behavior was intentionally added in by Ironclad in the original engine; can't be changed. You can micromanage your ships to stop and turn, but that's it. Difficulty has nothing to do with the "skill" of the AI; difficulty just increases the amount of resources the AI generates per second, excluding the unsupported Cruel and Vicious difficulties. Easy actually gives the AI a resource penalty, iirc. If the AI has access to good planets, then you can be sure it will produce ships to hit you with. The random generator in Sins doesn't particularly help in this regard; one's starting position can determine entire games. It's mainly to reflect the real difficulty in settling and controlling those planets. Plus, with the Extra Planets or Quick maps, you have a very solid logistics base to work with; 1-2 more planets can be all you need to get those labs. These planets can be useful for the sheer amount of resources they generate, or as a border/choke point to reinforce. Admittedly I did not design the planet system at all, that honor goes to NovaCameron.