I think that's so interesting.
I understand why they are opposites in Tris' time, but I don't think they need to be generally, and any other factions either. They became that way due to their exaggerations, one towards passivity and the other towards violence, but kindness and bravery don't exclude each other as such. I think having both aptitudes can help you pursue these virtues without corrupting.
I have posted before about ways each pair of factions is similar and opposite, so there's a lot to analyze. Some are obviously that way, like in the books, others need some deeper thinking.
These two factions, for example, share creativity, liveliness, they're colorful and loud. These people are likely to be open, interesting, vibrant. I think Uriah's other aptitude might be Amity, and I'd also say my mom has these two aptitudes.
