This. Every protection point lowers the chance of you receiving a critical hit by 2%. When you get to go to higher dungeons and missions you will notice monsters will crit more often... I don't know how damage calculation works but, ie a monsters hits 1-8 on you, but when it crits, you receive a full 40-50 damage hit.
Defense is "easier" to get from enchants (Rock, Defensive, Oak Tree, Burgundy Bear, Imp, Rigid, Captain... on top of my head) compared to protection. Equips will often have reduced protection if they're low quality (like 6/2, 6/3 Val or Dustin and unsigned Vambraces). So I would recommend the protection route.
Defence is calculated before protection. In most cases, even if the monster is going to critical you, it'll still have to go through the formula for defence first.
I find that at least 40 defence is necessary for hard mode missions. Because of this crazy statue that spits out bolts (Fomor's attack tara castle missions, which I also believe is not very popular in NA but we do it a lot here), which under most circumstances you cannot avoid getting hit.
The point about facing powerful mobs is still about not getting hit as much as possible.
Also want to point out that enchants adding protection usually means a sacrifice to max damage. Refined enchant for armors and burgundy bear enchant for gloves do not add any damage value.
As Phunkie said, protection is only good if you have a lot of it. Also, protection adding equips (like whatever sig items you said) are often expensive, and not many people can afford them and on top of that enchant them with good enchants. Since there isn't enough of protection to go around, most people would do well to go for more damage and defence.