Speaking of Poe and Rey, it is definitely something I don’t prefer, but I feel like I understand why Colin included it.
I think Colin wanted one of the things Rey had to deal with be the dilemma between romantic love and the Jedi path, and her not denying love was meant to be an acknowledgement of, “Love doesn’t make us weak, but strong.” The old ways of non-attachment and fearing love was counterproductive for the Jedi. Colin interpreted the conclusion Kylo’s arc in TLJ as definitively choosing the dark side, and the potential for that relationship ended. Since Finn and Rose were set up as a thing, it really only leaves Poe to have that necessary romance for Rey. I have a friend who ships them, so when I told her that it actually happened in Colin’s script it blew her mind.
I get why Colin felt a romance was necessary for Rey, considering her conclusion (I’m glad there was at least a reason for it), though I don’t think Poe was the best choice at all. I mentioned it before, but while Colin obviously had other plans for Kylo that complicated this, the Reylo thing actually seems to make the most sense here (like you explained) - especially when you just look at it on paper, bringing together the light and the dark. I would argue Finn makes more sense as well, considering Trevorrow treated the Finn/Rose relationship with only minimally more investment than JJ.