From its unveiling at Sony's E3 2013 conference to the release of its divisive DLCs to rumors of its sequel wiping away hundreds or even thousands of hours of progress, Destiny has had a very ... interesting life cycle. You could accurately describe Destiny as the best mediocre game to have ever existed, and yet it has fought off competing games (most notably The Division) and retained a fairly healthy audience over the course of three years—an impressive feat for any game. However, for all of Destiny's accomplishments and all of its faults, one can only ask "Can Bungie do better?"
After all, even the most devout fans of Destiny would be hard pressed to defend it against claims that the game is incredibly grindy, often requiring you to complete the same tasks over and over and over again for rewards that can best be described as mediocre. It can be safe to say that most of Destiny's existing audience simply accepts this to be a fact at this point, with no shortage of people (in LFG/PUG games anyways) often joking about how Destiny wouldn't be Destiny without a slew of rewards that aren't useful.
Yet for all their jabs at Bungie, and for all their hopes that Destiny 2 will revolutionize the gameplay, it can only be assumed that (based on Destiny's latest DLC, Rise of Iron) the core mechanics aren't going to change much. Sure, maybe Destiny 2 will have an actual story, or you'll get more places to explore, or maybe there will be larger missions and Strikes with more players in a Fireteam, but the same old grinding mechanics are unlikely to change. Simply put, even though everyone complains about the monotony and the bad loot and leveling system, it fulfills its intended purpose of encouraging people to keep playing the game (which is obviously good for the developer and the publisher when they want to sell you microtransactions).
Originally, you could reach a level where you are considered Raid-ready by merely buying vendor gear. Once you beat the Raid enough times, you could then hope to reach the maximum level via Raid gear. However, with Rise of Iron, this isn't quite so cut and dry anymore. You can still reach a level by which you are considered Raid-ready via vendor gear, but you will need to supplement it with another dozen or so hours of Strikes and such to get Ghost Shells, Artifacts, and who knows what else. Then, upon completing the Raid, you get gear that will (typically) only provide a small increase in level. Complete the Raid another couple dozen times and maybe, just maybe, you will be able to obtain the crucial thing that you need to finally level up one of the ten or so item slots that make up your level.
Needless to say, you could easily spend much more time playing the game with such a relatively frustrating leveling system, which is exactly what Bungie wants. Of course, Bungie could simplify things and make it so that there's more ways to obtain good loot without having to jump through so many hoops or provide more ways to level up in a more natural fashion (i.e. by playing whatever gametype that you want), but why would they when people are putting thousands of hours into Destiny as it is? Naturally, this would mean that Destiny will forever have the stigma of being "that game that you play because it is designed in such a way that it tricks your brain into thinking that it is being rewarded," but it works, and that's all that matters.
But you may be thinking to yourself "Wait a minute, isn't Rise of Iron basically a DLC that was made in lieu of Destiny 2? It doesn't seem fair to compare the two then." And you'd be correct in regards to the core mechanics and the gameplay; the sequel can change so much that it can play like an entirely different game. However, this doesn't change the fact that Bungie can still reapply any of the underlying design philosophies that were introduced in Destiny to its sequel because such philosophies work in their favor. They can still implement artificial (and seemingly arbitrary) soft caps that are designed to slow your progress to any of the reward mechanics in Destiny 2 whether it be loot or leveling; they can still sell you a mystery box of items (for real money) that don't even guarantee you a specific item; and perhaps most importantly, Bungie can and likely will try to encourage you to play the game as if its your job to keep up with the top 1% of the 1%, because there's just no reason for them not to.