I was not being a critic (as explained) and just stated that some classes would become 'depended upon' for content eventually.
 Well, I used to be pretty critical of GW2, back when I was still mad about no monks, but that's something different. I may have been snide about the 'lack of trinity' claims then, heh.
Hopefully, if some classes become too OP'ed, ANet will step in with balance updates.
If some classes are preferred but are NOT OP, then that is something people have to deal with. This can be addressed by ANet releasing some statistics on success/failures of high-end teams, and their team composition. If at high-end, teams succeed just as well with or without guardians, then the guardian effect can be attributed to personal preferences and biases rather than to imbalances.
It depends on how you're balancing really. You can't have everyone be capable of the exact same things, because then the game is stale. Making a support mesmer be on par with a support guardian would personally piss me off (as a guardian.)
Being slightly better at support than other classes is part of what gives the guardian its flavoring. Asking for all classes to have the same dps and support abilities across the board will just make the game zzz.
There's a fine line here, and arenanet is really close to crossing it. When does "class flavor" turn into "required class"
If there's only a supporty guardian, instead of 2 or 3... then the party should be able to say "okay we need sturdier party members and not glass cannons to offset" but that kind of thought gets flamed, because "you're supposed to be able to take anything you want" and while that I'd true, they meant "take any class you want" not "take a full team of glass cannons"
I'm rambly... I just woke up >___>
Sent from my Little Robot
This is nothing new, guardians have been asked to be in to this role since pre-release. It's just fractals are the only thing that become literally impossibly difficult. Fractals intentionally break the game design. It's an Apollo 13 scenario where you do things you're not supposed to be able to do. I don't care how that affects anything else in the game. No one ran SF sins in Chahbek Village HM, and requiring 3 guardians in CM SM is just as silly.
Agreed that high-level fractals is not a good model to balance around. Drop the difficulty a bit, and what is viable and efficient becomes different. Glass cannons are easier to pull off (and faster). Immunity is no longer required, given that you can survive hits. And so on.
About flavor, a big part of what makes flavor is gameplay, not what they can do. And even in what they can do, they do it differently. Mesmer will always be squishier and thus need to stay out of trouble, and make clones. Even if mesmers could output more support than guardian via shatter traits, phantasms, and making foes waste their shots on clones, there would still be a reason to bring the bubbles and melee damage. Likewise, when you need to do ranged damage, having a bunch of guardians really limits what you can do at the same time.
I'll just point out the irony of you saying "should reduce difficulty" on a dungeon that is supposed to get progressively harder as you go. >_>
The irony is that Fractals get progressively difficult in a particular way. If you increased difficulty in other ways you'll get different optimals, e.g. kicking people out on wipe encourages defensive play, adding boss enrage timers encourages high dps, increasing melee-range damage encourages using ranged weapons, etc.
There is no irony in saying that as you make something more difficult, people will flock to least resistance.