I don't see anything really unbalanced with the Core Turrets right now. Sure you can go wild with them, once you have 10-12 planets worth of energy. But getting to that point costs you 180 - 220 AIP. Not exactly free. Then there is the fact you have to hold the controller, keeping it safe, or hack it. Hacking them costs from your fab hack pool. This gets really expensive, leaving you with less hacks for actual mobile ships, all of which are technically exclusive to fabricators. (Either because its Mark V or experimental) There is also a bug that causes advanced constructor hacks to also cost a fab hack as well, making it even more prohibitive to hack all 8 of the controllers. On top of that, you have to find all 8 of the things. Sure you can get lucky and get the best of them near you, but I've see games where only a few controllers were within 4 hops of me, and the rest were deep in AI space, including one right next to a core world.
Now, playing a high AIP game, or Fallen Spire, does negate some of those draw backs. You're going to have a ton of planets and exess energy, so you might as well build them. You're going to have a lot of hacking points, due to the shear amount of AIP you have, so you might as well hack the controllers. But that is the point. You're going the high AIP route, especially with FS, so you get to play around more with resources. The downside is you have a metric ton of AIP and all that comes with it. And if you're going the FS route, you also have Exos coming periodically.
All in all, Core Turrets are powerful and incredibly useful. In a low AIP game, they can stop entire waves by themselves. But you have much more limited energy to place them around. In a high AIP game, or FS, you have much more freedom to place them, but after a certain point they are not going to just solo waves. And if you have ANY source of Exos, the core turrets WILL NOT stop those entirely. Might make a really nice dent, but not coming close to actually fully stopping an Exo. And the point of the Core Turrets, as with Mini Forts, was to allow better defending on the more open maps. This is something Core Turrets do incredibly well. All in all, I see no reason to make these changes. Core Turrets seem just fine to me. You either have only enough energy to place them where they are needed most, or you have so much AIP (and possible Exos) that Core Turrets alone wont keep you safe.