But there were four of them, several of whom were bigger than Peter; and they weren't just normal schoolboys, they were bullies. (It's clear from Peter's explanation that the other boys had baited him into fighting, which is something a normal schoolboy would be unlikely to do.) So I think it's at least reasonable to assume that the bullies had done the same to other people and were experienced in at least that type of fighting (i.e., prodding people into situations where they can be easily beaten up). No, they probably wouldn't have lasted a minute in a swordfight against Peter. But fighting with swords and fists are two different things.
Since much of the fighting in ancient and medieval times was done with swords/spears/clubs etc., Peter wouldn't have been likely to get involved in fistfighting on a battlefield. That sort of thing would only happen if he had lost all his other weapons. Never in the books or the movies do we see him fistfighting in Narnia. I'm sure he knew something about it, but that something doesn't make him Bruce Lee, especially when he's fighting four people.
Take this scenario: a bully bumps Peter. Peter is irritated but ignores it. Then the bully grabs him by the shirt and orders him to apologize. His friends are standing there, ready to back him up. Peter's private space is being invaded, his honor is being questioned, and he is furious; so he socks the bully in the jaw. But the bully's friends were already prepared to back him up. What if one of them got lucky in hitting Peter in the head at the right place? He would start out with a serious disadvantage. Or if the fight starts in a corner where Peter doesn't have much room to move about. All we know when the scene opens is that he's in trouble; we don't know anything else except that he's seriously outnumbered. Two to one would be bad; three to one is worse; but four to one? Great fighter or not, those are some pretty serious odds.
As for Andrew Adamson wanting to make Peter look inferior and stupid: I don't think that was the reason he caused the movie script to be as it is. I read an interview in WORLD magazine with Adamson discussing some of the plot changes he had made. His explanation for the changes with Peter was the fact that he started wondering how the kids would react to being so suddenly thrust back into the roles of children. (As in, what would a thirty-year-old do if he was suddenly made fifteen again?) Adamson said that Lewis never really answered that question, which set him to thinking about how Peter would react emotionally. Between that and the difficulty of making a movie out of a book like PC, he made some changes to Peter's character that he thought would reflect how a real Peter would react.
I think that Peter's reaction to a year in our world did not have to be the one Adamson set forth; but it was the reaction that some grown men would definitely have if they were shrunk down to the size of boys again. It's less "teen angst" than adult angst. Whether Adamson could have done things better or not (remember, Peter did lead his siblings wrong in one of the book's many sequences), his intent, at least, wasn't merely to degrade Peter, but to be realistic.
