Let's see... To start off, he's actually older than he looks, at least 28, for those who played Uprising should know... about the 25 year absence of Medusa and the 3-year time skip moment. Part of the reason why I mention this one is because well... I may say it a lot regarding my ship of Pit/Samus, but the problem people have been questioning me about is Pit's age... I don't wanna go into more detail than that regarding what some judgmental jerks think when I mention said ship and accuse me of being a certain something. So that's mainly why I bring up how he's at least 28 (not physically though). Besides, I hear that age is complicated when it comes to angels and gods, unlike humans.
Next thing I want to mention is Pit's not really um... dumb to say the least, though he is naive and a bit uneducated (I probably blame Palutena for that). Despite this, he is still a capable fighter as many of us know. There's also Chapter 23 where Pit's alone, and still fights through the dangers ahead. Identical to this, he's actually smarter in the JP version, but as many would expect, English butchering of dialogue, if I said that right, which makes Pit seem more like a joke than he should be.
He's actually been picked on a lot by most of the Uprising cast, mostly noted, by Hades, Palutena, and Viridi (mostly because of gods vs a simple angel). Despite the torment, he does try his best to get through things. It's also to note that even though he's often upbeat, he actually becomes very serious in Chapter 20, especially when it means trying to rescue Palutena; not a single joke. Pit's not all sunshine and rainbows, people. Dark Pit's existence, who is actually a part of Pit, is evidence (see KIU's Mirror of Truth).
She does pick on Pit a lot (including the sensitive "wing" part towards poor Pit and the "chapter 3 pheromone part"), and can be considered full of herself sometimes. It's likely partial due to being a Goddess (I assume many gods have some kind of ego) while Pit, who's an angel, is of lower class. This is probably common knowledge, but eh... it's probably because many seem to favor Palutena for her looks and ignore her personality and how she treats Pit sometimes. Despite all her teasing and such, she does care for him.
I should've done better with this. Then again, with how "open" and not serious KIU is, it leaves many questions unanswered.