It's not all about gear. It is a lot about practicing.
Some encounters seem trivial to me now, when they seemed just impossible on first tries.

My Paladin has 525 defense, 23.5k health. Nothing spectacular. I am not a good player, hyper casual, basically no experience of high level.
I nevertheless cleaned several heroics (Utgarde Keep, Culling of Stratholm, 3/5 Gundrak, 3/5 Drak'tharon). I just bought a shield formy Shamans for 35 Emblems of Heroism. Great feeling.

Trust me, practice the encounters. You will get some stupid repair bills for a while, but eventually, you will get better. It is you getting better that is going to make a difference quicker than your improving gear, actually.

And yes, a dedicated healer makes a huge difference. While you tank gets healed, 3 characters still DPS ...