Consider the classic standoff between an old man and a young man (both MAs.) It's quite obvious the young man has better physique. Does this guarantee a win?
My Tai Ji instructor had two simple sayings. The first one was "Age and treachery will beat youth and skill." In other words, physical fitness and resource availability are not the only deciding factors in conflict. The old man has a chance, perhaps a better chance than the youth expects.
The second saying was "Old masters fear the elbows of youth." Again, just because someone is cunning and treacherous doesn't mean they can't be caught off guard with a devastating hit from a strong, aggressive opponent. So the young man also has a chance.
Fighting is but one facet of conflict resolution. I'd say the person who gets into lots of fights may develop more physical prowess, skill and experience, but the person who stays out of fights may develop more nonviolent skills of conflict resolution - perhaps by talking, or seeing possible conflicts ahead of time and avoiding them, or manipulating circumstances to minimize the chances of violence.
If the fighter doesn't know how to make peace when they have to, and the peacemaker doesn't know how to fight when they have to, though... then they both still have stuff to train.