If I had to point to a "problem" it solves, I would say the problem of the Nightfall not really feeling like endgame content. Nightfalls became very easy in D1 after you had beaten everything else. Once you had all the guns in the game you could breeze through most nightfalls by running certain advantageous loadouts. Just as an example, Sepiks. For the first area everyone would run a shotgun of the appropriate element, breeze through, and then switch to snipers for the spider tank. The new locked loadouts combined with the new time limit for completion gives the nightfall new dimension that feels more worthy of endgame content.