The promise of AGI isn't really optimizing something mundane like widget manufacturing though surely it will be tasked with doing that. It's a rapid advancement of the frontier of knowledge. For example we dream of curing disease and aging but it is beyond our current knowledge.
Obviously nobody knows what that looks like or when or if we'll get there but there is probably a ton of existential hazards if we do. Shit even finding out things we hope for are truly impossible would be a kind of doom of its own.