It couldn't keep up that rate for 5 days flat.

Let alone start running again after just fifteen minutes' rest.

What? You can't just have characters say how they feel! That makes me feel angry!

Maybe that's why it reads as so cheesy and petulant to me. Reminds me of a little kid yelling "well I hate you!" because you wouldn't give them a sweet.

To be generous, I think that could be because Arya assumed that Eragon wouldn't be so callous as to attack his own species

I REALLY doubt it.

In a realistic situation we should expect this scene to play out like it is: an unskilled teenager being hopelessly outclassed by an adult who has had many years of training in combat.

It even says they both know how to kill with their bare hands (don't ask me when Ergy learned that) but are holding back. But you're right - it's a realistic depiction of a messy schoolyard brawl which shouldn't be there.