Here's the relevant changes:
- Savage Defense reduced to 35% of Attack Power from 65%. No longer procs from Lacerate tick crits.
- Bear form Stamina bonus lowered to +10% from +20%. Stamina bonus from Heart of the Wild lowered to +6% from +10%.
- Survival Instincts lowered to 50% reduction from 60%. Cooldown reduced to 3 minutes from 5 minutes
The first two are merely balance changes. However they also happen to be the ones people are most upset about. Why? Because people don't know how to lern2math before crying "OMGWORLDISENDINGBBQ!!!!11oneone"
Bears were massively overpowered in Cataclysm before these changes were made. I mean really, how could 20k absorbs triggered on crit not be overpowered? What about health pools 20-30k larger than other tanks? How is that not overpowered? It was actually so bad that tanks other than Bears were getting 2-3 shot by bosses. I mean if what you want is to be overpowered then fine, cry nerf. But if you want a game worth playing you'll know that's a really stupid idea.
The main opposition to the 3rd change comes from people that dislike "homogenization". Homogenization is necesarry for adequate tank balance. You can't design encounters to be equal for all tanks if some of them lack the necesarry abilities to tank the encounter correctly.