Quote Originally Posted by MetalheroD View Post
Why are you assuming that a tank HAS to wear heavy armor?
Because it's practical for a tank to wear heavy armor. Hence being called a tank.

Also, BLU's "concept" is that they use monster's ability.
...And for a Blue Mage to learn a monster's ability, they have to be attacked with that ability. Taking hits, and looking heroic in concept art and all, it fits as a tank.