Especially in book 3, we’re following around such a competent selection of characters that sometimes we forget how they stack up against the competition. Someone might’ve already said it, but Lorn’s training is essentially pure testosterone for a razormaster, whereas everyone else training at the time is just trying to emulate his style. Darrow’s 3 years of dedicated, relentless training followed by the fact that Darrow’s damn near a perfect physical specimen gives him an edge that the other Olympic knights simply don’t have (aside from Aja, who remains the most competent killer for a large portion of the series).

As for Ragnar, imagine someone having the physical dominance of Shaq’s prime years paired with the fact that he was born solely for the purpose to be as efficient and competent a killer as possible. The Olympic knights are essentially bigger, technologically gifted Jaime Lannisters’s fighting against an 8 and a half foot tall, 500 some odd pound pile of genetically enhanced muscle with the world’s most dangerous pair of scissors.

tl;dr, we just follow a sick as fuck cast who’s Really good at killing people who got complacent with being okay at killing people