Yes, every class is dependant on parties because it just works better, but mages become more dependant earlier on. Most other classes can support themselves, but a mage (especially on a non-range monster) would probably want to kill a monster before it reaches them and before they kiss the ground. They are nukers, but they also need support in "just in case" situations.
As for soloing to level 30, that should be pretty easy ... it'll probably take a long time, but it's not impossible. If it's really impossible, then there's something wrong.
As for weakness, they definately have not gotten weak. You're probably used to other games, like you said. A mage in any other game is guaranteed to be different, and probably in other games they're more powerful.
And, just one last thing. If you really think mages are weak and stuff, play all the other classes and just keep on leveling them if you have the time. That's the BEST way to understand how classes work. There are other ways to determine if a class is underpowered or overpowered, but learning it hands-on is probably the best way. A lot of our assumptions are probably pretty screwed, as we haven't taken the time to investigate all classes.
If you think mages are weak, try out some other class.
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