[Bardp1999]

The only classes who will be able to solo without high levels of gear will be Enchanters, Necromancers, and Shamans... and I guess filthy Bards. Druids and Wizards can quad but I am not sure thats really all that great past 55... Bear pits for Druids is incredibly dangerous and usually leads to more XP lost than gained.

Anyhow, even the 'good' solo classes typically duo or trio past 55 in my experience because you dont have to play the charm break game or worry about dieing as much.
Shamans with Epic I think have the easiest time of any class because its no brain rooting and mana-free DoTing... CoM will be littered with Epic shamans killing 5+ mobs at a time on the upper levels, and HS will be littered with enchanter/cleric duos.

But to your question Mages become less OP because Melee gets boosted from better itemization and your pets dont really scale up... and on raids most guilds wont even let you have a pet up because they can be huge liabilities with pathing so you become a summon/CoTH bot and nothing more in the end game.

Guild Leader: Summon more rods slave
Mage: I have 300 rods down sir
Guild Leader: Great! Now log onto a warrior/cleric/rogue so you can actually be useful to the raid... oh! and log your shit mage out in the corner so when we need to CoTH in more people we can
Mage: Yes sir!