Game AI system design pattern

I am creating a game where you have control of units such as workers.

The workers are individual instances who register to their observer (ai_obj)(which can be a singleton) . The ai_obj then delegates work from a priority queue. It will handle abruptly changing tasks before one is done and requeue the task.

That is the overall concept so far, but I heard from a colleague that centralised AI is not the way to go.

Any advice? I am looking for good and solid development pattern.