There's also the kind of ass backwards way the game encourages you to use them, from the perspective of an anti-micro tool.
Think about it. What worlds need least care from the player? What worlds could you happily hand off to the AI without worrying it's going to make a mess of things?
Your home-world, and your oldest colonies. One the layout of the tiles is decided, all that really needs doing from a management perspective is upgrade buildings once the tech becomes available.
And which worlds need most care and attention from the player? Your newest colonies, the young outlying worlds, recent conquests and that one planet you colonized a long way from your space for Strategic Reasons.
And what worlds does the game encourage, even require, you to keep as core worlds and which ones to assigned to sectors?
That's right. The ones that least need the player to look after them have to stay as core worlds and the ones that most need the player to look after them to have to be farmed off to sectors.
And if you don't do it that? If you put your most developed inner colonies into sectors so you can micro your new colonies, then... that's your most productive worlds flinging resources into oblivion, isn't it? As well as your best space ports hidden behind the Well Of Torment, also known as the Planets and Sectors window - probably the most obnoxious fucking UI element in the game, after the create new fleet window. And that kind of micro trickery is firmly discouraged by the stupid 25 influence cost** you get for removing systems from sectors.
It is not just AI bugs, the whole concept around sectors is just... wrong. It doesn't work. They simply don't do what they're supposed to do. They're supposed to reduce frustration***, but all they do is increase it. Multiply it, even. Anyone else put off colonising planet number 6 because it means you'll have to start dealing with sectors? I do. And I don't even like micromanaging things. I like the sector concept in principle, and I'm not bothered by not being able to min-max every last planet. I don't even like the tile system; the tile system is probably my single biggest problem with the game, but I'd still rather deal with it than bloody sectors.
The entire system - tile management, sectors, the whole economy - must be reworked. Not tinkered with around the edges. Not just adding more options for the sector AI to only enslave aliens on a Tuesday and build robots when the moon is waxing gibbous. Not more AI fixes. Completely reworked, so it adds to the game and doesn't detract from it.
* I know you can give sectors resources, but they give you absolutely no feedback when they're short on monies so you have to keep manually checking the fucking "Planets and Sectors" window, which I hate with a furious passion.
** otherwise known as the 'fuck you for trying to play our game' mechanic
*** oh and the fact that the planetary management system is frustrating is also a problem that needs to be addressed