Tom
Istar
Humans are physically the weakest of the great apes by far. A chimpanzee tore a woman's face off and tore off her hands. That was on Oprah. A bear killed a man by decapitating him with one swipe. That was described on Ray Mears' bushcraft show. Individual humans only do well in fantasy when writers make him quasi superheroes like Paolini did with Roran. Realistically ain't no human general leading from the front. Especially not a King. In terms of endurance, we're good in the real world, but when humans go up against fantasy creatures in general, humans really have to pick their battles and stay in their league to avoid being ROFLstomped.http://4.bp.blogspot.com/-QdLxF3BjEPQ/VcoDoJhmLJI/AAAAAAAA3Gg/uia6juCi6Kc/s640/bloodthirster.PNG
Because when you start giving humans superhuman abilities like magic etc, you aren't writing humans anymore, you're just writing another fantasy race with the human label.
I think humans are a lot better equipped for fantasy than you give us credit for. We may not be the strongest, but we're incredibly resilient, inventive, and highly adaptable. Those are our main strengths. Despite being unable to go toe-to-toe with larger species like bears or other primates, we have a number of inherent advantages. Endurance is the biggest--our ancestors survived by persistence hunting, a method in which we simply followed prey on foot until it was too exhausted to keep going. Our gaits have a crazy energy curve that allows us to spend less energy switching between gait types for rest, owing to our unique ability to modulate the way we breathe (which is in turn a perk of having no weight-bearing limbs attached to our ribcages).
In fantasy, we're also not playing with real-world rules. The term human is very subjective in the fantasy genre. People who can use magic are (usually) still seen as human. Humans may live longer, be stronger or faster, or have other inhuman traits, but they can still be considered human. I started a thread going on here a while ago, actually, where we discussed just when fantasy humans stopped being human. It seems you can stretch humanity quite a bit before we become unrecognizable--our most distinctive traits, after all, are not our physical abilities but our psychology. It's true that it can get a bit ridiculous when you take our natural abilities into the realm of the implausible (like Roran in your example), but I think humans can take almost anything the fantasy genre can sling at us with a little grit and ingenuity.
(Besides, kings and generals have no place leading at the front anyway. That's just some inaccurate ridiculousness, not evidence of human inferiority.)