it isn't just the person: If some1 is a good athlete then they may have an advantage - however when they fight, whichever style they do thay'll revert to a specific style (street fighting etc), a kind of universal one or they will fight with what they know but it would be the specific style(s) which are realistic. SO although it's something like 80% the person, 20% the style the style can, and generally is the deciding factor - if it isn't good they'll put themselves at a substantial disadvantage. To make up for a faultly/ineffective/unrealistic style they will revert to a version of a good, effective style but they'll just be unskillful at it. However because they're using an effective style, however bad they're at it, they can still hurt the opponent - the superior strength and/or cardiovascular factors just add to the fighter. The more skilled person, although weaker may still be at a greater advantage if their overall Health isn't much worse. Even if it is alot worse, the skill of the person or fighter may oevrcome sheer atheletisism. Especially if it suprizers the better conditioned person.