I get the impression that you have about equal chances of getting a rude gate agent no matter what airlines you fly with. Which is to say they're almost all reasonable people, but sometimes have bad days, other times it depends more on how you ask. The guy here seems to have an entitlement. He's a frequent flyer, his kids aren't, he was asking if they could get on with him in the early boarding. He could have paid the early check-in fee for them and gotten on before most people anyway. I think it's $15 on southwest. Point is, he had other options. It's fine to ask for favors, but if you're fuming about someone NOT granting you a favor, you're probably the asshole in that situation.
I posted this above, but in my experience, when Southwest announces boarding procedures, they almost always include a special perk for families traveling together that they can board with the family member that has the lowest ticket. This might not be fair, but it is something they have always done in the past both in my experience and the guy in the article's experience. Now the guy was probably upset and embarrassed, so it's entirely possible he wasn't entirely honest about how rude the attendant really was, but I want to be sure the part about family boarding is clear.