I think the problem is that it's far too easy to actually dictate where the battle is fought. The people who refresh maps over and over until they can get a good chokepoint are honestly somewhat boring players who always stick with the same thing rather than the idea of just playing with what the game gives you (the intended way). On the other hand, even if you aren't playing with Exos, you can still very easily force most waves to attack the same planet just by killing warp gates and it's so easy to actually do that.
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Try playing a 8/8 or above game with Spirecraft, Golems, Botnet, and FS active (Minimum of 4/10) at the same time with a single champ and Hybrids 4/10 and Advanced Hybrids at 10/10. WITHOUT A CHOKEPOINT. This is how I enjoy my game. Its not boring. Its a chaotic mess of unholy death smashing (and several times just devouring) the last hope of humanity. And besides, when done right the point is to move your choke FORWARD as you expand your empire. (Even more so when you're using FS and HAVE to expand your empire further out to continue the story)
Even at best when I have a large amount of teritory I can take in a "backwater" behind my choke, its because my chokepoint is my homeworld. Sure its a fortress filled with all sorts of ways to slaughter the AI horde mercilessly, but its also the only system the AI has to actually kill. They only need to get lucky once, and I have to remain lucky all the time. And hope the Z-trader comes around before the really nasty things do. Because 10 Spirecraft Shieldbearers covering a few golems, an H/K or 3, some Dire Guardians, and you don't want to know how many Starships and fleetships show up on your HW and/or your chokepoint and you do NOT have an P-Inhibitor, there are NOT enough static defenses to keep you alive. Even if its not your HW that falls in that rush, you have things like the Shark kicking in and the craziness gets exponential from there.
Rolling over and over again to get a chokepoint that you can start at may seem boring to you, but when you're playing with so many things turned on at 8/8 and above, you are going to NEED that choke. And when you get the Spire involved, you are going to need to expand forward to a new one.
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Personally I am all for the per planet cap idea on turrets. Drop the number of allowed turrets on any world to 1/3 or 1/4 of what it is now, and allow Core turrets to be built with normal turrets sounds like a great idea. Combined with something that allows for the current number of turrets to be built on a single world, with that structures cap at say, 2, while NOT allowing Core turrets on any world with said structure sounds perfect to me.
And yes I feel you need to make the cap 2. Any more and it becomes WAY too easy to build turrets everywhere (assuming you can afford them). But making it 1 will mean you can only have 1 major choke, and sometimes you need at least 2, plus it allows that if you DO have a single point of entry you can eventually move that point forward without having to completely give up your current choke, at least until the new one is up and running.
I also agree that the structure needs to be permacloaked, and to have AOE immunity as well, so it doesn't get targeted and doesn't just get blown up by random fire. This way you don't have to give it a ton of HP and have the AI waste shots on it. Or you COULD just give it a ton of HP (like P-Inhibitor levels of HP) while giving it a targeting priority so low that the AI might as well just ignore it.