I'm having the same issue. I've got over 70 hours now, I queue with friends in Emissary and I perform well in my matches. I've been winning a lot recently, but my rank has not moved at all, while theirs goes up every win. Have the devs said anything about this?
My match quality playing solo is horrendous, which is a real bummer.
EDIT: I finally ranked up to Initiate 2. My friend with a 37% WR ranked up 5 times in our session tonight up to Seeker, so I don't think WR is the sole deciding factor. I tend to have high damage and healing in my games, I also have good KDA in a good amount of my games. Could just be he's an outlier, but still.