There's a sense in which they are. Rand wanted her heroes to be perfect. So, it would not be enough to give Howard Roark his single-minded passion and rationality; she also had to have him be right in his choices.
Rationality can lead to the "right" conclusion in the sense that it is the conclusion that all the available evidence, known to the decider at that point in time. points to that conclusion. Unfortunately, this is not how reality works: rationality does not lead to coming to the "retrospectively-right" conclusion 100% of the time. Rational people have to re-evaluate, correct mistake, an change path all the time. This is something that Rand's writing misses.
Further, humans are not rational in every moment. We are rational animals... not just rational "beings". Our rationality allows us to be alert about our "animal" impulses and our irrational biases, and allows us to correct conclusions and actions that arise from them. So, once again, the process is not smooth.
If you look at some of Rand's positive characters: Rearden is often used as an example, but you have Dominque and Steve Mallory and so on... then Rand does give them some flaws and idiosyncrasies. But, she seems to have had this idea that the hero should be flawless.
So, if you want to look for a Howard Roark in the real world, ask yourself if the real world has got people who have a single-minded vision, and pursued it against contemporary advice, and had to fight all sort of battles, but came out vindicated and successful in the end. Turn on the NPR "How I Built This" podcast, and you should find a few examples.