1) Same level doesn't mean equal in power since you could still upgrade your subclass. Someone can hit level 8 in 4 hours but they will still at a disadvantage because people had 36+ extra hours upgrading their subclass and getting those extra abilities. 2) The fact that you remembered the plot of the Strike mission rather than the actual story mission (the Hive is about to invade earth) proves how horrible memory retention can be when time passes.