Ok. Can someone explain in detail the differences between these two modes? I know level advantages are enabled in Iron Banner and not in the Crucible... but exactly how are level advantages defined?

In the Iron Banner, the "Attack Rating" number of your guns and the armor ratings of your gear affect how much damage you deal and recieve. In the regular Crucible, they do not.

Thanks. I figured that was it, but it wasn't explained very well in-game.