That's not necessarily a bad strategy, especially if it the AI can pursue this path by planning multiple moves in advance. I used something similar when attacking my enemy in that "other game". I could have just plowed through the system in a straight line to get to my target (the enemy's main shipyard), but that would have likely ended in my destruction, as there were some serious defense posts in that straight line approach. So instead I did a more involved flanking manuever (in 3D space, no less), which was "the path of least resistance" and incredibly effective. If the Thargoids follow a similar strategy, then that's pretty impressive. If they just look around and say, "Oh, there are tough humans on the skirmish lines, let's just stay put." then that would be a bit disappointing IMO.The devs kind of already told us, their entire war effort boils down to "path of least resistance", which places them at an IQ comparable to a locust swarm, or a swarm of zen Buddhists (little joke, don't hang me).
I would also like to think that Thargoids have some sort of either bigger or secondary goal than to just wipe out humans. For example, if Thargoids are moving in such a way to occupy all AM systems first, there's a logic to that which adds to their realism. If Thargoids are just 3D Space Invaders, well that's kinda boring.