At first look the 20% decrease physical damage taken look awesome and don't get me wrong, it is nice but after further thought I think it's more of a quality of life change than a huge buff.
First of all a vast majority of damage we take as tanks that is physical is dodgable. That being said, on average, this 20% buff only applies to 55% of the damage we take while we have Savage Defense up. Therefore on average when we hit Savage Defense we will only take 11% less physical damage (55% change to be hit * 20% reduction). Therefore in my mind Savage defense is now 56% physical damage reduction.
Further to my comment about a quality of life change, say we have a bad Savage Defense and dodge zero attacks. So now instead of our rng dodge we will always take at least 20% less damage. This help with the "getting gib'd" that avoidance tanking can lead to. Here is a chart for an example of a 1.5 melee swing timer mob for one Savage Defense.
Total Damage Reduction During A Savage Defense.
|# of Hits||Old SD||New SD|
As we can see this just brings up the bottom end of Savage Defense which was really needed to make bears a more stable tank.