Instead of Rey developing close connections with Luke, Han and Leia, while basically Poe and Finn never develop a close relationship with any of them, maybe it would have made more sense if each of the three new characters developed a mentor bond with one of the old characters. For example, Han could have met Poe, Luke trained Rey and Leia been like the mother he never knew to Finn. Or something along those lines. It might have meant they got more character development. However they'd need to come up with some reason for Finn to be hanging around. He's just absolutely useless. Poe's not much better either.
I really like this idea, and a simple way to make Finn actually useful would just be to have the other cast members
not be as good at shooting things. Like, literally, he's an ex-stormtrooper, how hard would it be to make him the best shooter/infantryman in general in the group? Or maybe he's got some medical skill or whatever from his time as a trooper, or they come up with some actually reasonable reason to have them infiltrating a F.O. base in which case he'd suddenly become REALLY useful (if they ditch the "I was the janitor" joke line, anyway).
Of course, that edges into my dislike of the idea that the Resistance is for any reason separate from the Republic and everything they did to make it yet another tiny group instead of, say, pulling a trick out of the various stories in the EU where it's just some of the Republic's stretched and limited resources fighting a single warlord with, like, one powerful ship because the rest of the Republic Navy is urgently needed everywhere else, etc.
Then Poe could
just be a hotshot pilot, Rey could just be the up-and-coming Force user, etc. And if you throw in the mentor characters, not only would it make a lot of sense but it'd also be a really cool touchstone to the older movies, and if they avoid the kill-the-mentor tropes better we wouldn't even have to watch most of our favorite characters unreasonably die for really poorly constructed reasons!