You can't compare the representation and talent balance of sub-85 classes to that of endgame. Simply put, a hunter at level 24 is subject to a very different PvP environment than one at 85. It's like saying that if a child is capable of reading "The Cat in the Hat," he should be able to read "Othello" too. While the basic capacities are there, you miss the complexities.

For the most basic example, at level 24, hunters have http://www.wowhead.com/spell=781 (Disengage)- one of their most powerful and most frequently used defensive abilities, even at 85. At this same level, Warriors have http://www.wowhead.com/spell=100 (Charge), which allows them a gap closer if they are not in combat, but not http://www.wowhead.com/spell=20252 (Intercept,) which works in combat and only becomes available at level 50. Thus, if a hunter disengages, an attacking warrior has no available gap-closer at 24 and just has to chase after his target. To say that this is representative of the PvP interactions between a Warrior and Hunter at 85 is simply wrong, because both classes have more abilities to contend with one another. It's like a scale- as an ability is added to one side or the other, the balance shifts to favor one or the other. The idea is to have both sides equal at 85, but this is often not the case.

You mention that other classes also don't fare well when in range of melee opponents, and while it is true that a Mage/Warlock/Boomkin/etc does not benefit from being close to a weapon-flailing melee, these classes also doesn't lose all ability to dps because of it. A global cooldown has to be used by their attackers to interrupt casts, but it doesn't cost a melee anything to just stand on a hunter who has been snared or slowed.

In addition, you missed the point about focus- the complaint was not that classes shouldn't be able to column-kite to avoid damage, but rather that when an opponent uses LoS on a Hunter's Steady Shot/Cobra Shot, the Hunter loses both the potential dps of that ability (something suffered by all ranged classes) in addition to the loss of focus regeneration (which no other class has to deal with.) This cycle is doubly troublesome because the loss of dps a moment ago is compounded when the Hunter is now focus starved and unable to afford more damaging instant shots.

Next, you're right that Hunters have a niche. That's not the problem though. To get an invite into a RBG or high rated arena team, you need a strength that other classes don't bring. The problem is that while we have plenty of utility, our abilities are often redundant and other classes have much better options for the same result. Silencing Shot = Silence/etc, MM AP Buff = DK AP buff, Freezing Trap < Poly/Hex/Blind because a target has to wander into it, etc etc.

In brief, endgame does not equate twinking. Twinking is about maximizing a small number of abilities. Endgame is about balancing a comparatively large number and maximizing synergy. While we hope that the abilities of all classes are balanced in relation to one-another, the general consensus is that hunters are poorly balanced and need some rethinking.

If you want to get invited to the party, you have to be pretty. Right now, we Hunters have a big, ugly mole. With hairs on it. The bright side is that maybe with a little surgery, we won't make small children cry at the sight of us for all the wrong reasons.