I wouldn't consider many of these points a flaw of the community but rather the way the game is designed. Sure, you could go for a diversified party but why would the average player want to take that risk when he can play it safe and be rewarded exactly the same? The most obvious solution would be, of course, to balance the classes and make content which doesn't cater to any specific set of roles. I've still to find a company with the aptitude to do that however.

Another failing I've found in this game is the Materia system and the way equipment is handled in this game. As was stated in this thread, Materia is purely based on luck and the amount of money you possess. This would be fine, a nice little addition and money sink so the wealthier players could have a small advantage. As it stand though, it's practically a necessity to have double or triple melds on your equipment to be considered well-geared. And that's just for one class, potentially millions wasted for one piece of equipment for one class. Other than that, you can get the AF gear which the community as a whole seems to regard as sub-par or... well, as far as I've seen, there's no alternative. Either have money or bust. At least the primal weapons seem to be on par or at least not completely horrible compared to melded items but we all know the drop rate on those.

Why talk about this? Well, from my observations this system just widens the gap between the "elitist" players and the "casual" ones. You're either well geared or you aren't. There's no in-between. And, frankly, a system which relies so heavily on money and not on group coordination or player skill for gear rewards is simply shameful.

For last, I do agree on the point that you should not need to have all classes leveled to be considered useful, but again, I do not see this as the communities fault but rather as the game. There's a very important thing called versatility. Why choose one player who can perform a role when you can choose another which can perform all roles? Another facet of this is needing certain skills from other classes for certain jobs. For example, you'd never invite a BRD with no Stoneskin or a WHM with no Sentinel. But, again, this is no fault of the players but rather of the current job system.

Bottomline is, the community simply adapts to the unique mechanics of the game it's playing. If those mechanics are flawed, people will not go out of their way, nor will they hassle themselves to do it "the way it should be done". This isn't an utopia. You can't expect a perfect community in an online game but when the game is flawed at such core principles so too will the community be even more than it should.