I haven't seen plant growth dense enough to warrant more than a few minor deviations, so I'd have expected a "rough" path that the AI returns to after dealing with local obstacles. But I've only done some simple scripting; nothing on this scale. And if it's affected by the visibility of plants, I'd be interested to see if longer draw distances get better results.
It's the straight line thing that gets me the most. Try to move NNE and it will go NE until it lines up with the target, then goes directly N, even on an open field. It simply won't follow a straight line unless it lies on one of those 4 axes. That just seems like lazy maths to me.
"But I'm sure it'll get better some day," says my EVE-addled brain.
@Devs: Love you guys! Keep fighting the good fight!