In my opinion Iris is good character contributing to balanced and interesting group dynamic with writers attempt of keeping her past and story like goal,problems surrounding her pokemon etc in mystery until now being nice twist trying to keep audience in intense mood.
Currently she is getting pretty good treatment for a supporting character screen time wise(especially lately)giving us insight in her back story and past life,what motivated her wanting to become dragon master,as well problems about her pokemon like Axew,Emolga and Excadrill until lately being addressed.Inclusion of rival like Langley is welcomed thing too which serves fitting as push/motivation in her future development.
Insight in past and defeat she experienced from Drayden pretty much sets up that culmination of Iris development is going to happen around 8th gym getting rematch with Excadrill with Axew being petty much a given being main center of Iris story with her mission being to raise and evolve it in powerful Haxorous.
I also like the fact that we get for a change experienced trainer who isn't complete rookie which didn't happened since Misty with Iris showing impressive skill with her result of 99 wins winning tournament under age of 10.