Oh, I see. This is a better question for Light but the short version as I see it is that everything you guys interact with or fight scales with the party's average level. for example, a "bear" would be a low-level enemy, but as you get stronger we might make you fight a "bear" that's stronger than before so it feels like relatively the same challenge. Eventually, you'll encounter different types of "bear" that have special attributes that make them more difficult than the party average, providing a greater challenge at higher levels. So basically it depends, but as far as comparing your character to a regular person just think of yourself as simply having a set of skills a normal person wouldn't necessarily have and therefore slightly "stronger" than them. This difference is expanded upon every time you put ranks into skills, becoming a more adept fighter/magician.
As far as the running example goes, that is a case-by-case scenario so you'll have to check the skills and see for yourself when we've finished the skill list in the glossary. One example I can give you right now is a core skill called Adrenaline. It is a fairly advanced skill on the Health Mastery tree, so it will have somewhat high prerequisites to even start putting ranks into. The effect at each rank is quite noticeable though since it's max rank is lower than some of the "easier" skills before it. It is a triggered skill that activates when your character dips below 15% HP remaining, and when that happens at rank 1 your character instantly restores 50% of their Stamina and Mana. At rank 2 it restores 75%, and rank 3 (it's maximum rank) it restores 100%. On the other hand, a simpler skill like Restoration on the Stamina Mastery tree goes up to 10 ranks but simply improves the rate that you naturally restore stamina each round.