The main advantage is that you can immediately distribute fine-tunes to all of the copies. This is much higher bandwidth compared to our own low-bandwidth/high-effort knowledge dissemination methods.
The monolithic aspect may potentially be a disadvantage, but there are a couple of mitigations:
AGI are by definition generalists
you can segment the population into specialists (see also this comment about MoE)
https://www.lesswrong.com/posts/aH9R8amREaDSwFc97/rapid-capability-gain-around-supergenius-level-seems also seems relevant to this discussion.