Well, that is a good point. I'm certainly open to discussion on this point. My main thoughts, with the system as-is, would be:
1. Set up defense-in-depth, with your best defenses on the bottleneck behind your bottleneck. Then when the AI comes crushing into your first bottleneck, you can crush them back. Let's call this the "honeypot" approach.
2. You can indeed go out and sweep through the adjacent planets to kill the AI preemptively. Since all the AI ships would be clustered around the wormhole right next to the planet they are considering attacking (though rather sparsely), this shouldn't be an enormous chore, but it leads them to fight you in their territory, and they may well retreat, etc.
Now, regarding what could be changed about the system:
HKs as Siege Breakers
With the hunter/killers, it's possible those should be lone-gunmen type of ships like raid starships, etc. So they are highly survivable and come crushing into your system past the normal siege ships, blasting up your defenses. You'd have warning of them being created, and they'd come from the AI homeworlds, so you'd have some time.
Pros: you don't have to look for the AI; it's possible that if your defenses are truly awesome at the bottleneck, you can maintain it in a fairly automated fashion; the other AI ships that aren't replaced by an HK can then join in the attack if it's sensible to do so, or maintain the siege if it's not.
Cons: it might make things much harder; it might lead to the same sort of AI-impaling-itself-on-your-stuff logic that used to be there; it's very unforgiving to planets that are not enormous bottlenecks, thus unintentionally encouraging super-bottlenecks even more.
Ideally, players won't create super-bottlenecks that can withstand tens of thousands of ships. When they do that, that creates problems one way or another. Either it's impossible for the player to lose, or if the AI waits until the AI has overwhelming force against that, then it's impossible for the player to win. In the past it was just the first case, I quite like the addition of that second one.
It's a tricky question, though, no doubt. Let's wait until we see the HKs in there before we go too far with further changes, though: since those will be centralizing firepower, so to speak, that might make things more interesting. Also, there may be some other bug there presently which is causing the threat to stay very high longer than it should, with those ships way off in the middle of nowhere. With Spikey's save, I think a lot of those threat ships are attached to Hybrids, but there still dont seem to be enough bordering his planets. I need to look into that more and get that cleaned up before we can really see how this siege-type mechanic effects the game properly. It will feel really different just from these upcoming changes alone, I think, and then it would be easier to decide on what further, if anything, needs to be done.
