That is actually not true at all. I'm tanking Stratholme Undead, Emperor in BRD or Dire Maul North with 21/0/30 just fine. Yes, zero protection talents.
- Holy Shield is a talent for threat generation, bosses and big groups only, it's a waste of mana on single targets. It costs more than your seals+judges and it only gives a -chance- that something will actually happen.
- Blessing of Sanctuary is only for aoe tanking. Most of the time you're much better off with Wisdom and Kings, simply because reducing 350 damage to 326 damage from one elite doesn't really help much.
The issue at high levels becomes aggro. When your party, especially warlocks start gaining lots of spelldamage, you will have trouble holding to your mobs. The simplest way is just to let your group "chill" at the start, however most people start pew pew even before you do. Salvation is not almighty either. The solution is to grab some spelldamage, the easiest slot to use is your weapon and
trinkets.
Start with a judge-reseal is the best way to gain the initial aggro. Marking targets properly will help aswell. If you want to save mana but keep your AoE aggro up, I recommend grenades or farming
Crystal Charge. Keep your RF up at all times. If your onehander is slow, you can try using Seal of Command too, but it's not reliable.