supp guys idk if every knows this but defensive stance grants 25% damage red. shield wall glyphed grants 60% damage red. and demorilizing banner grants 10% red. thats 95% damage red. lol plus you will have a shield equipped
No it's 1 - (0.75 * 0.4 * 0.9) = 73% damage reduction. And shield doesn't do anything except add armor.
By the OP's math, if you thunderclapped the mob would heal you for 5% of the damage it meant to do.