I understand your point on the ease of having one currency and the complexity of having 5. However, if the game was set up this way, we would have more control over the gear we get and at what level it drops. For example, if you're looking for a FWC chest armor, you would rank up, get FWC marks, and purchase a chest piece from the cryptarch guaranteed to be what ever light you are. It would lessen the grind a little. Probably not much, because bungie would just make it hard to rank up with a faction or reward only a few marks for the rank up. Even so, it would allow us to increase the power of the gear we want with fewer set backs. Ultimately we would level up no faster, but it would be more straightforward.