No, alphas are not necessarily big and bad and brutish. But some guys that are never try to be anything else.
It’s just a way to observe natural social structures and interactions that humans have engaged in for thousands of years. It’s just a model for understanding those natural social connections and behavior that can be observed in all groups.
If the model doesn’t work for you or you’re not familiar with the comments, don’t use it. But it does work. Individuals are all different, of course, and nothing like this can explain specific behavior, but in general women are only sexually attracted to alpha males, or men they see that way.