Depends on what you mean by “perfectly isolated computer”, there are already methods for exploiting air gapped systems, an AI would be able to figure out more and more complicated exploits.
Theres also the “air conditioner“ argument, where a schematic could be given to someone to build a machine that does X, but in reality it does something to benefit the AI. I also think memetic exploits exist, interrogation/negotiation techniques seem to imply they do, and given a certain amount of time (which you imply would be allowed. Communicating with “select humans” implies a continued contact, not just one conversation per person) an AI would be able to psychoanalyze and exploit personality flaws.
Another problem with this is "economic theory" is not monolithic. There are different schools of thought within economics, and applying economic theory No. 1 from X school might imply completely different things than applying it from Y school. Economics is a fractured, competitive field of concepts to say the least. Go listen to an argument between Neoclassical economists and Post-Keynesian economists and see what they agree on.