When i read the small part in the original post about not being able to complete “yellow quests” solo which are non-group quests, I began to wonder how you play.
Not all classes can actually complete yellow quests solo that require multi mob killing in a short period of time. Classes like Warriors have a hard time if you dont understand their abilities to the fullest and use them accordingly. On top of that you can’t just go in and hope for the best.
Questions I would like to ask are:
Are you using potions, scrolls, sharpening stones, getting stuff enchanted and using the many professions to your benefit?
Are you aware of each races special abilities and use them properly?
Have you ever leveled to the maximum possible and understood the class at that high end level?
You only get better by playing more and more, not only do you gain experience in dps/tanking/healing in dungeons you gain the experience in battlegrounds.
When I was a noob, I didn’t have much knowledge of my class nor all the others. As I played more and more on ONE single character to the maximum level, it all began to make sense. The role of the warrior in pvp and tanking all came naturally. At that point getting better didn’t require more playing but rather came with the use of macros, keybinds and UI customization. My twitch reflexes are good it was just a matter of mastering the class I chose to stick with.
I pvp’ed plenty in pre Burning Crusade to the point of getting the Grand Marshal title. PVP is a whole different world. Not only do you need to master your own class, you need to know exactly what is the counter moves to all the other classes. Knowing how to beat a rogue on paper is all fine and dandy but all that knowledge needs to be practiced in gameplay. I can know that killing a rogue is all a matter of disarming, demo shouting, hamstringing, mortal striking, etc… but can I press those buttons in a timely fashion while constantly moving so I’m not a stationary pylon that gets beat up on. Practice does make perfect.
I suggest to you that you stick with one class, learn that class to its fullest, and play more in the areas you think you lack in skill.
One thing you should know as a hunter is the term kiting. If you dont know what that means, it’s simply keeping your distance from the mob/enemy. You should be firing your shots while moving away from the enemy, concussion shot or wing clip and keep your distance constantly. You achieve this effect best when you aren’t using the “S” key (or back pedalling/ walking backwards slowly) you need to be able to use your mouse to turn around in an instant, shoot arcane shot a sting, while holding still to get a normal auto shot in, then moving away till the mob dies.
Again stick with one class, learn it, get better.
If you can try to find an in-game mentor to teach you the ropes while playing. And if you can make 4 friends, 1 tank, 1 healer and 2 other damage classes and run dungeons together often. Dungeons are a great place to get item upgrades.
) in order to make guns and accessories. (Well, my mom would say it would be better to gather herbs & leathers and make money that way but she’s sort of a tightwad in game. 
)