Leon is better than Chris at hand to hand. In RE5 gameplay it appears as though Chris and/or Sheva can defeat Wesker at hand to hand, however, most of that is due to gameplay.
Do you serious expect the creators of RE5 to make Wesker move at super fast speeds so you can't even respond to it? NO, so they HAD to slow down Wesker's speed for the shake of gameplay.
Also what happens in gameplay is "possible" not guaranteed, meaning playing differently results in different gameplay scenarios. Its not as canon as the main storyline of the game. What happens in gameplay terms can only be taken with a grain of salt, best way to interpret Chris defeating Wesker in hand to hand is if Chris had to he can DEFEND against Wesker's attacks to prevent Wesker from killing Chris, but cannot defeat Wesker in hand to hand.