This change makes no sense.
Unyielding Sentinel is the Epic Destiny for tanks: 'Unyielding offers great durability, a new taunt mechanic and some powerful healing tools. The playstyle has become more active rewarding attacking with only intermitted blocking. Useful for pure tanks or anyone looking to increase their survivability.' - your words.
Now you want there to be other tanking options.......... and you are going to achieve that nerfing Unyielding Sentinel. So where does that leave the balance for Unyielding. It has nothing else going for it. Nobody is in that destiny for healing believe me. The only characters who get the tier 5 enhancements from it are dedicated tanks (If anyone feels like chiming in with.....'well my nuker sorc runs T5 in US' - I'll put my 'You're doing it wrong response' right here, in advance).
What are you going to give to Unyielding Sentinel in exchange for the nerf to hit points. The tree has little going for it as it is. Why would anyone go to T5 other than for the hit points - 20% buff to hitpoins, plus the 5 quality in Deific Vengeance plus the 10,000 hit point clicky. taking away 10% percentage points of the 25% base hp buff bonus is a huge nerf to an underpowered destiny.
If US is not the tanking destiny, nobody is going ot take more than a splash in it as it stands