Yeah but he was talking about specifically using spirecraft penetrators to do it. They can pretty much go anywhere in the galaxy with impunity since they are perma-cloaked. So destroying an AI command station on the other side of the galaxy is entirely possible with them. That said, don't you have to actually capture the world with spire civ leaders on it to get the negative AIP or does it happen just from making the world neutral? And will the AI attack them in that case?
I other people have confirmed that the AIP decrease happens even if the planet they are on is neutral (something that most certainly be addressed, the current system is way too abusable)
However, any defenders the AI had on that planet upon the destruction of the command station have a pretty good chance of going on the offensive, even if the planet is completely across the galaxy. Plus there is the normal AIP increase of killing a command station, which for 30 AIP for destroying an AI command station (25 for the command station, 5 for the warp gate), which will take a bit of time for the reduction to start paying for itself.
Also, there is the risk of triggering a raid engine or alarm post or some other AI structure that does not like being next to a neutral planet.
Plus, the Spirecraft penetrator is blind, so you won't even be able to see where the command station is (and thus can't target it) unless you have scouted there before. (Unless you are playing on complete visibility, of course)
So its a cool strategy, but not one without risk or need for setup.