Genetic engineering and cybernetics would make a machine that could smash Conan without slowing down. This is what always makes me call bullshit on 'the outer demons have to assume an Earthly form' in the Conan stories. So what? They could make themselves nanobots or invincible carbon-vanadium-iridium tanks. There's nothing other than plot reasoning to make them so weak - certainly Set could figure out how to build a hydrogen bomb after a few billion years. Hell, a college physics student and a couple of engineers could do it, now that the principle's understood.
This has always been the most glaring plot-induced-nonsense in a Howard story. Generally speaking I go along with much of it as semi-realistic, if a bit fantastic. But anything that can travel through dimensions and form complex, combined biological machines can VERY EASILY build a tank. Or a nuke. Or a supercarbon, hydrogen powered monster that could literally kill everyone on Earth by itself (given enough time). I guess you can rationalize it with some sort of superdimensional pact, but in that case why are modern humans allowed to be so much more powerful than them?
Lovecraft doesn't often have this problem. His truely outer-monsters (as opposed to Earthy-Alien stuff) really could just rip through human beings like carbon paper. So why doesn't Conan have to fight a Colour Out of Space? The only answer I can think of is "because he'd die and Howard didn't want to write that story".