Classes don't have to be balanced at all in P&P or RPGs.
Besides, you can easily argue Fighters always were balanced in AD&D: wizards would never become as powerful as they do without them to carry them through the first bunch of levels - incidentally, the most interesting levels.
This doesn't take away from the fact that classes should be balanced throughout the game. Classes shouldn't be "low-level classes", "mid-level classes", and "high-level classes." If you advocate that, then you should advocate respec. At higher-levels fighters should be wizards. And this is exactly what happens. People start to multiclass because they start to realize how little their class can offer.
Level 5+ fighters are far from useless even though they of course don't hold a candle to wizards. But then they have had to suffer through levels where they had a grand total of 3 crummy spells to cast, along with HP rolls that ensure instant death during the early game should anyone trigger a trap or even if they just catch an errant arrow. Balance.
Then I would suggest BALANCING the classes so that while they play differently at all levels, they are effective members of the party at any level.
It's like fighting games. If they were balanced properly they'd have 8 characters only: Ryu, Ryu, Ryu, Ryu, Ryu, Ryu, Ryu and Ryu.
...one of the best parts of older D&D is that wizards become out of control. One of the most fun things about it, actually. Don't break with tradition, especially one that works so well.
WRONG WRONG WRONG WRONG. Fighting games ARE balanced in that each fighter plays differently! The only unbalanced fighter that is famous for his imbalance is Akira! The other fighters all play differently and have different tactics involved with them. If they weren't balanced in their differences everyone would play Ryu - especially at tournament and pro levels. This isn't the case at all. Dhalsim, Zangief, and Ryu all play differently. Some are closer combat, some are further "long-distance" combat. They totally play differently. Ask any good Street Fighter player.
You're wrong.
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I'm not sure how you guys feel about this, but some of those shitty RTSs that spawned games like DOTA figured out some of this stuff and I'm surprised that D&D still hasn't. There are a bunch of different heroes in those DOTA games (and Warcraft 3, its predecessor) and they all play differently, with different abilities. And some of them, like Warcraft 3, have leveling concepts. Yet, there is no "good" hero to choose from - or an imbalanced one. Each one plays differently, but has a use.
The only difference is that D&D is a much more complex game and has to maintain balance over a wider range of choices that players can make - wider skills, classes, levels, ablilites - there are a bunch of switches and levers in this crazy machine that we call D&D. This is difficult, yes, but it is also what can make an RPG so much more interest as a tactical combat scenario.