Well youre missing a whole lot of externalities in your thesis, like assuming it will be mostly plastic, which is not feasible if oil production plummets due to global warming, or if we all die because they dont stop massive oil demand.

If the time horizon is 30 years until mass production, then titanium may be cheaper than plastic if we can effectively mine the moon by then. If it's 10 years, then the AI probably isnt ready yet.

We would also need reliable hydraulics that arent dependent on fossil fuels, and those parts cant be plastic anyways. If you want mass production of robots ASAP then we need to produce a lot more oil and that will probably kill us js.