Originally Posted by
Shippuu
You're right, Auron wore robes mostly, but his "katana" was also a greatsword as well. But even then, let's take a look at Auron.
He was the guardian of summoner Braska, and caretaker of Tidus later. Auron's specialty are the break abilities that lower enemies' stats, and guard abilities to shield his comrades from enemy attacks. His early stat growth is based around high Strength, Defense and HP.
Hmmm....Defends/shields others, has high STR, VIT, and Defense...what role of the trinity has emphasis on those traits I wonder? So he may be lightly armored in appearance, but in practice he's definitely in line with being a tank. The same goes for Bravely Default's Swordmaster.