Humans aren't superintelligent, and are still able to design macroscale technology that can wipe out biospheres and that can be deployed and propagated with less intelligence than it took to design. I'm not taking the bet that you can't shrink down the scale of the technology and the amount of intelligence needed to deploy it while keeping around the at least human level designer. That sounds too much like the "I can't think of a way to do this right now, so it's obviously impossible" play.