Ravens will probably challenge in the AFC for the next few years. I think they walked off the field against the Chiefs w/ the mindset that they could beat them in the playoffs and have traditionally went toe to toe w/ Pats. Other than spending a little too much on the secondary they are really sitting pretty cap wise and can keep the team together. Nolan is the perfect OC for Jackson and Brown is going to be an excellent No.1 WR.
Jackson also unlike Watson, Darnold, and Mayfield has a good OL and Ingram has been running well (granted against lousy Ds).
Other than that I don't really see and up and coming teams in the AFC. Maybe Denver if they can find a QB, maybe Buffalo if Josh Allen (who might turn out to be a functional QB) can continue to improve. However there is no reason to believe either of these things will happen to the degree where they'll be a legit threat.