Well, it's good to know that the sector AI is moddable and people are working on it. Right now I am using a mod to give me effectively infinite core worlds because I absolutely refuse to play a game in which I am forced to turn over my hard won planets to an AI with the IQ of a carrot. There are major downsides to sectors with ethics divergence, factions and even rebellions... The least we should be able to expect if we are going to suffer those consequences from using sectors, is that they will at least build properly.
Sadly, at a certain point I wind up with SO many worlds, that micromanaging their building becomes truly tedious. At that point, I pretty much quit the game.
Yes developers, the sector AI is SO BAD, that I would rather not play than use it.