That's not a fallacy, it's simple fact.
We'll have to disagree about which facts are obvious then.
I've run many, many games with wide power spreads where the players still all had plenty of fun. Or look at games like Ars Magica where party power imbalances are built right into the system.
But those two statements don't necessarily support the claim that balance is unimportant because the GM can ensure everyone has fun.
Somehow a lot of people still love and play the game anyway.
I would argue that they love and play the game because either the game itself addresses story balance in some fashion (the 'troupe' system) or else because the game master or group addresses the game systems lack of story balance by imposing a lot of unwritten house rules on the system. When you examine these games in play, you find that characters disadvantaged by power achieve story importance via unwritten character powers that the GM imposes and respects. For example, you may observe that per the results of play, some seemingly weak character has figuratively written on his character sheet something to the effect of "If it is funny, it works." or "If a favorable coincidence happens, it happens to me." Or often you have an unwritten rule like, "If a player isn't having fun, the GM throws him a bone."
Being unwritten components of the system, does not make them less important aspects of play at a particular table. It just makes them more difficult to translate between tables.
In other words, the GM is often desperately creating balance where none otherwise exists. Even then, that's not always sufficient. Consider how Ars Magica evolved and fleshed out the notion of a grog as a viable player character to make a player who had took a grog role have more interesting things to do and a greater role in the story. Or you may have a game triumphing despite its rules, not because of them, only to find that in the long run its depending only on novelty and continual game reboots as people keep trying to have the game they want to have, not the game that they are getting.
I never really heard balance whines until the folks started trying to bring MMO ideas into RPGs.
Just because you personally don't have the experience, doesn't mean that your experience is indicative of anything on a wider scale. One of the main reasons I have found all of White Wolf's story teller games utterly dysfunctional in play is that they had no balance. A player that created his character in an optimal fashion could utterly dominate play, and given the dark themes of the setting and the conflicts implied by it, this amounted to utterly dominating the other players. This required basically that non-optimal characters built primarily from a story perspective have stories that involved them being abused, dominated, and forced into submission of characters with more raw power. LARPs in particular had this sort of problem in spades and required extremely tight control by the referees over what sort of characters which though legal could be allowed into play. People had a lot of fun, but everything was always balanced on the knife edge of destruction and only herculean efforts by story tellers or story telling staff kept everything from going off the rails. Things only got worse when it became usual for players to want to play characters from different source books. Even when players were generally cooperative, White Wolf stories tend to get undermined by the lack of balance and the fact that the balance (such as it is) isn't interesting. For that matter, I had even more extreme problems with Amber diceless gaming for the exact same reasons.
Honestly, if you never heard of balance problems prior to recent comparison with MMO's, then I can only conclude your primary experience of role playing was with a small group of close friends whose unspoken social contract establishes base rules for how story will be shared regardless of system.
But for RPG's it's just not. I've seen far more fun removed from RPGs in the name of balance then has ever been added.
This vague anecdote doesn't inspire confidence, and in any event, it's just an anecdote. I would say the exact opposite. Virtually every time I've seen a session move on the scale from 'meh' to 'unfun', violation of the Fundamental Law has been the core issue. Rules can be meh. Stories can be virtually nonexistent and if existent make pulp fiction look classy, coherent, and well framed, but if you have a player who with or without the blessings of the rules violates the fundamental rule "Thou Shalt Not Be Good At Everything", then your game is crap.
Going a bit further into my assertion, I honestly believe that it's the lack of this precise game component that is responsible for older children and certainly adults eventually giving up on the notion of role playing as a pastime. All small children naturally role play. The way small children get away with it is that they aren't actually playing together, but playing beside each other. Contradictions with each other's story and incoherence and continual changes in the fictional positioning and the fact that the story doesn't really advance doesn't bother small children. Eventually as they get older and their intellects mature, and their social skills and ambitions increase, and their imaginations soar, the frustrations and arguments as players jockey for theme, fictional positioning, story direction, and ultimately rank in the social hierarchy of players drives people away from such pastime. What's missing is precisely balance. It's balance that made RPing into a something adults could do together. And the reasons and ways White Wolf campaigns in my experience tended to break down were precise mirrors of how elementary school age RPGs tended to break down, precisely because the systems actually failed to assist with balance sufficiently.
