I mean yeah there's no strong scientific basis. But they do describe real life phenomena albeit in a very simplistic way.
The terms just seem like corny speak for men that are more "manly" and men that aren't manly (and are instead "soft" and sensitive).
We can't act like there aren't distinct pockets of men. I mean, look at how most older male virgins, incels, etc. All have VERY similar traits: social awkwardness, sensitivity, physical weakness, low self-esteem, shyness, low confidence, timidity, etc.
"Alpha" is usually just shorthand term meant to refer to guys who are "the man", usually very confident, assertive, has leadership qualities, isn't too sensitive, usually strong, and is taken seriously and respected by peers. Think of the most popular dude in your high school.
Obviously it changes by context.
In short: alpha is a man that meets most markers of masculinity, and is treated and rewarded as such. (He is respected, and gets perks).
A "beta" is someone who doesn't meet those marks, and thus is either disrespected, ignored, or fails to get any perks.