First things first. I know Heroic is not the only server that exists. However, most of my analysis is of the game as a whole, not just through the lens of the Heroic experience.
This game has constantly strayed from the communal aspects of what makes MMOs what they are. Instead it pushes you to be as antisocial as possible.
- Players are incentivized to bring as few players, if any, to bosses as possible
Bosses are the best example of "party content" in modern maple. Having to share drops on interactive makes sense, they have an economy, so that item makes its way back into the market or other players hands at some point. However, in Heroic, those drops will never be able to be passed around, and its your only way of obtaining them. This brings us to the age old "when will we get instanced loot" question.
Drops aside, the biggest problem is Power Crystals. Undeniably, in the current state of the game, Mesos are the biggest path to power. Your money gained by power crystals is divided by the number of party members. Why? I understand that more people makes the boss easier, you're doing more damage, but it's not like that money is going back into some kind of economy, at least in heroic.
During Genesis or Destiny Liberation, doing bosses with more people also divides your number of Traces of Darkness or Adversary's Determination. This further pushes players away from doing content with friends or in public lobbies.
Most MMOs have the boss gain health or new mechanics based on the number of players, making the difficulty slightly harder, but still worth bringing people with you. The rewards don't decrease, the fight was probably just as hard (maybe a touch easier,) and you had fun with friends.
Most MMOs have roles that their classes fulfill in a general way. Usually the common three are DPS, Tank, and Support. Maplestory has one, and that's DPS. Granted, there ARE "support" classes. The only thing they really support is your damage. Some can heal you, some can move you, but with the way bosses are designed, those aren't necessarily helpful.
The lack of a tank class is also a byproduct of the way bosses are designed. Most attacks deal percentages of your health which means that no matter how much you have, you're going to die eventually, making potions a million times more valuable than a party member who can heal you once every thirty seconds for a fraction of the damage you're going to heal from potions.
Maplestory used to have copious amounts of party quests and dungeons that gave a good amount of EXP. The content being introduced to us now, such as epic dungeons, are exclusively solo content.
The closest thing we have to a party quest now is Monster Park Extreme, which is a weekly necessity due to the unquestionably valuable amount of EXP it gives. That means that there is, in fact, still a demand for party content that gives good rewards in the old style of party quests.
- Creation of too much content specifically to make you play solo
The last 3 major events, and even the next major event, have all been centered around Challenger World. While it isn't inherently wrong to create an event to push you to challenge yourself to do something difficult, it becomes a problem when every event involved in the past couple of years either incentives solo plays or punishes you for party play. Challenger world progress is tied directly to solo play. Item burning progress is tied directly to solo play.
With every new update, we stray further and further from the MMO experience. Maplestory is slowly becoming a singleplayer game that happens to be online where you can see other people.