You are talking as if every dollar that RIO was to lose or make...

You are talking as if every dollar that RIO was to lose or make in the project was less valuable to shareholders.
Returns are returns. Obviously, they could fund losses / standstill periods for longer, but that comes at a cost and every BoD is accountable for that.

Saying "On the CAPEX front, again it's completely irrelevant" just points to a complete misunderstanding on how financial decisions are made.

Are you really saying because the project is small relative to RIO's balance sheet, numbers don't matter? they'll be happy to loose as much as it takes to get to production and/or not hitting their returns once there?

RIO is in the same game as any other developer against incumbents. Either they've found the way to ramp up with unit costs <10kpt or they'll press the brakes at some point.