Again I say, if SE made items drop 100% of the time every kill and you could cap out on gear in 6 kills, it would be no different than if you needed on average 15 kills to get every item. Why? Because on average everyone will kill it 15 times, so the average person who starts 3 months after its out, will have to kill it 15 times, just like the average person when it first came out, and that means that the majority of people will probably not get it if they started late. At the same time, if its 100% always, then theres a chance that someone will go back & assist, they know theres a good shot at you getting what you need, so their time wont be wasted, and they are not playing with nothing but luck. If you make it super luck based, people are less likely to go back for that reason, and less likely to help others, instead of helping and keeping it alive I think it more often than not hurts those who are slow to catch up because no one wants to go back & deal with luck to help a friend get something.

Another way to go about it would be to adjust the rates to be better every update, but that requires constant upkeep, and SE cant afford to do that these days on this game.