Hmm, your argument makes sense. My basis on Sokka being an ENTP was based more on comparing him to Jet (he's has way more charisma and grace in his style) and his inventive side. I didn't really base it off of functions thoughAny type can be goofy. It mostly depends on the levels of the functions. Watch the show and you'll see him all the time have intuition inferior moments. Half his comedy comes from those moments, where he doesn't understand something so he just writes it off as unimportant. ESTP are more than capable of coming up with ingenious plans, especially one who embraces Ni which at the end of the series he has.
And as for being clumsy, ENTP's aren't necessarily clumsy. I'm my own example here. I almost never fall down, ever. Even when something is super slippery, because I'm always ready to fall at any moment. Most of his clumsiness comes from his lack of understand of what will happen next. Look at episode 1, he is constantly living in the moment he is in, never really thinking things through to seeing what will happen next.
I think this will help with the argument.