Normal and Heroic dungeons are still there. Still just as relevant as they were in Vanilla. Which is to say, relevant when you're leveling and first exploring a new zone, and mostly forgotten after. But you can still keep playing those if those are your jam. No judgment here. Have fun!
What M+ has done, for most of us, is make dungeons relevant for entire expansions. For most of us, M+ is right up there with Transmog among the greatest innovations in history of WoW.