Personally, I think confidence matters, but its not the confidence that gets these "alpha" men the ladies. It is their good looks. If a guy is good looking, they will get attention from the ladies (particularly in the formative years of ages 11-15). After getting enough attention through their adolescence, they will naturally get confident. Then, everyone sees these confident and assertive guys getting ladies, and people "oh, it must be their confidence/assertiveness that gets them girls." Nope, it is their good looks that gets them the ladies; their confidence is just another thing that is the natural result of being good looking.
I don't care what anyone says. If my ugly self suddenly was really "confident" and "assertive," girls would still not like me. You have to have a REASON to be confident, otherwise its not true confidence but just fake showing off that girls see right through. I'm ugly, I'll deal with it, and I'll adjust my dating prospects accordingly. But don't tell me or my ugly colleagues that it's our lack of confidence (like we have some mental defect) when it is really a physical defect we have no control over (asymmetry, small muscles, etc.).