40% isn't much in the grand scheme of things, but maybe they can reach higher reduction with more research/materials. Mass and power are pretty cheap for spaceX, so shipping more solar panels and a heap pump might not be a deal breaker.
Would e.g. a reduction of 90% in radiator area change the overall picture on the overall feasibility? I think not, it would still be ludicrous, but I'd be happy to be proven wrong.