Every barrel on any gun (AR, bolt action, AK, lever action, whatever) wears as it is shot. The amount of wear depends upon the conditions of when it was being shot, how hot the ammo is (all ammunition erodes/flame cuts to some degree), and just how good of metal the barrel is made of.
If one has a rifle that is a (for speaking purposes only) safe queen, then the barrel life can probably be measured in a couple of human lifetimes. If one has a hard use rifle that sees multiple high round count excursions, is practiced with alot, and is subjected to generally speaking hard use.....the life of all components are affected conversely. By this measurement, a barrel should be looked at as a "use" item, along the lines of magazines. Magazines are not considered to be lifelong items either on a hard use weapon, and I can guarantee that a barrel is subjected to much more stress than most other firearm parts that are looked at as usable items.
The best part of the AR platform is the relatively easy ability to make changes to necessary components as compared to other platforms: bolt actions, lever actions, pump action.....etcetera.