Challenges are there, if you look for them. Raids are harder and more challenging than before, there are way, way more mechanics to be aware of and to master. Any player back in vanilla would have been overwhelmed by today's complexity of encounters. Brawler's guild offers some unique challenges as well. You can also try to solo old raids, e.g Lich King 25 HM is no easy task solo. LFR is supposed to be a pushover, it exists solely for the casual masses.
You, like so many others posting comments about WoW going casual make the fallacy of false dichotomies, i.e assuming that the addition of casual content somehow makes it mutually exclusive from established content. We now merely have more choices as gamers, that is all.