A lot of Seddit posters makes it out that mellow guys get no pussy and all alpha men are just asshole tyrants running rampage.

You can be a friendly guy but still be alpha.

A beta nice guy will use extreme 'nice' tactics in efforts to win over women (which rarely works) because he has subconsciously placed her value above his. A beta nice guy can not face rejection well as he is not assure of his own self. His self image relies on external validation. Think somebody like Mike Wazowski for example.

An Alpha nice guy is super confident in who he is but doesn't think he's superior or puts others down. Usually is loved by many due to his friendly nature. He respects others but also respects himself. These kind of guys will show friendliness through demeanour rather than by doing women (or people in general) favours. They still joke around and tease girls but its all light hearted. This guy won't bend over backwards just to get sex, its more like a 'what you see is what you get' offer with women. If he gets rejected its fine, if the girl digs him then great. Think John Cena or Anthony Joshua for example. Respectful and friendly people that are confident mentally strong alpha males.

An Alpha asshole likes to think he is better than everybody, is incredibly rude towards others especially women. Respected by many but hated by more. His confidence is incredibly high but is basically arrogance. Alpha assholes are masters at sparking emotional roller coasters within women. This male archetype probably get laid the most from what I've witnessed. Think somebody like Conor McGregor for example.