Your dad apparently doesn't know anything about Aikido. He also doesn't know much about self-defense, either.
He says something about twisting an arm. I'm guessing his idea of self-defense is everything to do with boxing (striking only). What he doesn't know is that an Aikido-ka first applies Aiki, then applies jujitsu (or whatever style the Aikido-ka knows).
If the drunk got his arm twisted, and the technique were applied properly, it is likely that the arm, wrist, or elbow would be broken, or that the shoulder would get dislocated. That's a lot of hurt.
Some people get the idea that Aikido is all about static and take-it-easy practice. That's true for beginners. But the senior students apply aiki to their own style (which in Aikido's case is jujitsu).
Tell your dad to go challenge a sensei at a good dojo. I think he'll get the point soon enough. And if the sensei lived by the tenets of Aikido, he'll have your dad buying the first round of beers.
EDIT: one more thing... No style is good against any other style. Only stylists can be good (or bad) against any other stylist. But your question is also asked by many who do not understand kickboxing and Aikido (and many martial arts). Kickboxing is designed for sport. Aikido is designed for self-defense. Kickboxing techniques can be used for self-defense. And there are Aikido-ka who compete (their style is called Tomiki).
Also, you don't block anything in self-defense. If you're going to expend the energy to stop someone's incoming strike, then, you ought to go the mile and break whatever it is that they're throwing at you. But don't block it. And as for countering, yes, we in Aikido have what we call "atemi" - a sort of pre-emptive strike. It's meant to distract or confuse, in order to use the opponent's momentum against themselves, and to use the opponent to redirect or stop himself. Other than that, avoiding a fast kick generally means moving out of the way. That's what we train to do: move out of the way, then off balance and throw or pin.