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Not to be sarcastic, but out of curiosity
There're many explanations on why no restriction on class composition is bad or Tank/DPS/Heal
is bad, but not much talk about good potential that these systems can make the game more fun
and encourage grouping.
When soloing, all classes must be able to level up similarly, but suddenly in groups,
certain classes are assigned into certain roles that players never had to do
while leveling up in solo. ie) Tanks don't level by tanking and heals don't by healing,
only DPS can do its party role in solo by killing mobs.
In solo leveling, any class dps, dodge/mitigate mob's attack, and restore oneself
ie) drinks HP/MP potion
Players like to solo because they can do them all, but doesn't want to group up
since they're confined to certain roles which is definitely a personal preference.
Extreme specialization of a party role onto a certain class limits gaming experience
unless each player chooses to create many alts which are confined to other roles.
Abandoning this class composition requirement makes sense. It can consist of tank/heal/dps,
but only if one chooses to based on personal preference.
Traditionally bosses are very dangerous mobs that require tanks and heals for DPS to
take them down effectively.
This also limits the maximum output of a party to the lowest common denominator out of
the three roles. So by designing dungeons and boss fights which cater to non-trinity
restricted party, we can avoid these cons of trinity system.
From what I've seen in the EQN gameplay video, players "faceroll" through boss attacks
ie) no one gets oneshotted, but disabled temporarily from combat due to CC effect of
that boss attack. If players dodge it, they have the advantage of attacking
while boss cannot counter them for a short time
Not having to worry about dying makes the party less prone to failure/wipe
and focus on the fun part (take down the boss)
A giant sandbag for players to beat on makes the party more united
than blaming each role of a failed attempt.
Combine CC from all party members and they can lock down boss and make it possible
to DPS from all sides.
If this makes the game too easy, boss can always be made harder
by not giving a tell sign or make them ridiculously faster so that
players can't DPS without using their survival skills.
This means players don't have to do the same dance every time
to avoid mechanics of that boss/dungeon.
In other games, once players know the mechanic, it becomes too boring,
so devs raise the bar, but at the same time make it too hard for newbies to even attempt;
they either quit the game, or buy gears so power creep can carry them through endgame.
Not fun at all
To me, smart bosses that mimic a strong player similar to 1 vs 10 PvP is more fun
than beating a stupid robot.