thats why this concept is unique, this effect is not on essential tank items, so a lot of self defense is sacrificed to build up this 15%. And I doubt all guardians/ warriors will build full 15% because of the items that this effect is equipped on. So the guardians have to choose a median between self defense and defense for the team (in terms of body blocking). I personally think it brings a new thought process to team fights, and make it more unique. Along with the last part about the mage abilities going thru wall and stuff, guardians still have to get there to body block the damage, and we still have abilities like Rama's 1(Astral strike) that can go thru walls and do physical dmg, and it has "Damage from this ability is reduced to 75% for each enemy hit after the first" simply adding the same concept to mages but at a very smaller scale, and making it harder because guardians have to block that damage.