The essential complexity isn't solvable by computer systems. That was the point Fred Brooks was making.

You can reduce it by process re-engineering, by changing the requirements, by managing expectations. But not by programming.

If we get an LLM to manage the rest of the organisation, then conceivably we could get it to reduce the essential complexity of the programming task. But that's putting the cart before the horse - getting an LLM to rearrange the organisation processes so that it has less complexity to deal with when coding seems like a bad deal.

And complexity is one of the things we're still not seeing much improvement in LLMs managing. The common experience from people using LLM coding agents is that simple systems become easy, but complex systems will still cause problems with LLM usage. LLMs are not coping well with complexity. That may change, of course, but that's the situation now.