Some weakness are obvious: Lennie is a few knives short of a cutlery drawer; Crooks is black and crippled; Curley is short; Curley's wife is, well, a woman. Only a few characters in Of Mice and Men seem to rise above their subordinate positions by being willing to pull the trigger when no one else will. But is there more to strength than wielding a gun? Do Slim and George avoid weakness through force of character as well as firearms?
You can't win in Of Mice and Men: the weak are pitied, and the strong are condemned.
Steinbeck suggests that weakness is better than strength.