Quests hell

[Niwashi]

any MMO is a game about competition

There are some MMO's that focus on competition. This isn't one of them. Its group content is mostly cooperative, not competitive. But it certainly is focused a lot on group content. Its not possible to play solo for long in this game, like you can in many other MMOs.

why should I play alone 2 or 3 months in an online game, I feel that this is not the right approach.

Then why would you play alone? Looking at just the level 50 content (since it seems to be the level 50 quests people complain about), there's:

Dungeons:
Castrum Meridianum
The Praetorium
The Wanderer's Palace
Amdapor Keep
Pharos Sirius
Copperbell Mines (Hard)
Haukke Manor (Hard)
The Lost City of Amdapor
Halatali (Hard)
Brayflox's Longstop (Hard)
Hullbreaker Isle
The Tam-Tara Deepcroft (Hard)
The Stone Vigil (Hard)
Snowcloak
Sastasha (Hard)
The Sunken Temple of Qarn (Hard)
The Keeper of the Lake
The Wanderer's Palace (Hard)
Amdapor Keep (Hard)

Trials:
The Chrysalis
The Steps of Faith
A Relic Reborn: the Chimera
A Relic Reborn: the Hydra
Battle on the Big Bridge
The Dragon's Neck
Urth's Fount
Battle in the Big Keep
The Bowl of Embers (Hard)
The Howling Eye (Hard)
The Navel (Hard)
Thornmarch (Hard)
The Whorleater (Hard)
The Striking Tree (Hard)
Akh Afah Amphitheatre (Hard)
The Minstrel's Ballad: Ultima's Bane
The Howling Eye (Extreme)
The Navel (Extreme)
The Bowl of Embers (Extreme)
Thornmarch (Extreme)
The Whorleater (Extreme)
The Striking Tree (Extreme)
Akh Afah Amphitheatre (Extreme)

Raids:
The Labyrinth of the Ancients
Syrcus Tower
The World of Darkness
The Binding Coil of Bahamut - Turn 1
The Binding Coil of Bahamut - Turn 2
The Binding Coil of Bahamut - Turn 3
The Binding Coil of Bahamut - Turn 4
The Binding Coil of Bahamut - Turn 5
The Second Coil of Bahamut - Turn 1
The Second Coil of Bahamut - Turn 2
The Second Coil of Bahamut - Turn 3
The Second Coil of Bahamut - Turn 4
The Second Coil of Bahamut (Savage) - Turn 1
The Second Coil of Bahamut (Savage) - Turn 2
The Second Coil of Bahamut (Savage) - Turn 3
The Second Coil of Bahamut (Savage) - Turn 4
The Final Coil of Bahamut - Turn 1
The Final Coil of Bahamut - Turn 2
The Final Coil of Bahamut - Turn 3
The Final Coil of Bahamut - Turn 4

PvP:
The Fold (Light Party)
The Fold (Matched Party)
The Borderland Ruins (Secure)
The Borderland Ruins (Slaughter)

And that's not even counting the fact that all the earlier dungeons are also still available, and in several cases include loot that's desirable at any level, so that adds another 12 dungeons and 4 trials. Plus it only lists instances, not open world content, though the Hunt is usually done in groups as well.

Along with all this wealth of group content, there's also quests, at least some of which can be done solo, others of which require one or more of the group instances. But unless you focus mainly on crafting and gathering (which are the only other major source of soloable content), there's far more group content than solo content, no matter where you are in the game.

The presence of a few soloable quests does not make the whole game solo. And there's nothing wrong with an MMO providing, or even requiring, an occasional brief tidbit that people can do on their own. You're still going to be playing in groups the vast majority of the time unless you're actively trying to avoid it (and a significant amount of the time regardless of whether you try to avoid it, since a lot of the group content is required).