1. I do not think every people person is necessarily superficial. Liking people does not mean you always sacrifice your entire being or interests. Now relating to functions strictly, the extraverted functions do come off as more superficial than introverted functions. Some more so than others.
I think Fe as a function has a higher CHANCE of being superficial, because they care so much about finding harmony, they will follow the crowd for it. They'll sacrifice their own interior values they may have if the majority doesn't share them. I think there is a chance INTROVERTS can come off as superficial as well, by keeping their values and views internalized and not showing them to other people. They may smile and nod, but think everything you're saying is bullcrap.
2. Se is a very superficial function. It is impulsive and lives exactly in the moment. If someone is an Se dom/AUX, I think there is a higher chance of being superficial. I think this is the function that would feel the most superficial to a person. Maybe this is just my view, but someone who sees things solely in the moment is not a deep thinker. they won't think of consequences, and they may be more likely to simply follow the lead rather than lead the crowd.
3. Te would be somewhat superficial. "Thought" I think is hard to call a superficial function. They both think, just in different ways. One thinks in the form of finding a result, the other thinks for the sake of thinking moreless. But in general, Te is not as "deep" as Ti.
4. I have a hard time seeing the intuitive function in general as "superficial". Ne/Ni involve thinking deeper into the future or into creative outlets. If someone is intuitive, I feel they're less likely to come off as superficial, unless they are flightly in other functions. Their thought process would simply appear less shallow.
So I am going to lean toward some kind of ESxx