I started in BC about halfway through and I was a prot warrior and because I was coming in fresh my gear was full dungeon/rep blues with no PVP gear, crafted epics, badge items or raid items.
I had 12k HP with full gems and enchants and it wasn’t until I got some S2 PVP items, badge gear and Sunwell patch items like the vendor shield and stam trinket from Magister’s Terrace that I got up to 15k or so.
Raid tanks in T5 might have 15k.
Heroic mobs hit like freight trains on blue gear. It was super rough