Explained, Healer (50% guard + 20% intercede) 70% damage reduction, Attacker ( 30% damage reduced taunt).
Healer and jugg Hold where other tanks fall in pvp.
I'm not a tank but i do know your math is wrong there, when you add another percentage it doesn't add like 50+20=70.
so like 50% of 100 is 50. if you put another 20% on that, it is 20% off of 50 (which is 10) so it is dropped to 40. another 30% would than make 28 (30% of 40 is 12). just trying to clarify stuff, cause the way you explained it is the healer would not receive any damage for a small amount of time which is not true. but after all is said and done, that is still a lot of damage reduction.