For the second time, Predators hunt humans for sport and armed with the bare minimum. Their challenges are a means of improving their weapons and tactics but it's purely for sport.
If they were up against Iron Man, they wouldn't come in with just a shoulder blaster and a spear. They would come suited up with whatever advanced technology they have.
The post about Predator killing Pepper Potts is pretty spot on. They're hunters, not comic book super villains. Forget about that, tie you up and tell you a monologue bull shit to give you time to escape. They'll shoot you through the skull while you're pissing.
When Iron Man was getting drunk in college, Predator was cleaning up an entire crew of private military badasses that had toured various countries in conflict on rescue missions. (We're comparing Tony Stark of today's Iron Man to Predator in general). As seen in the 2012 movie Predators, a lot has changed in their technology.
