Personally, my issue is not so much that DKs are getting a battle res. It's that they can use it while tanking, and I (as a feral tank) can't.

A Blood DK main tank will be able to say "I'm going to reposition the boss so I can res PlayerX," do so, hit their button, and go on with the fight.

A Feral tank has to have an available off-tank to take the boss, or they're almost guaranteed to die in painful and messy ways upon dropping Bear Form and casting Rebirth (boss downtime mechanics and epic healer cooldowns notwithstanding).

Ferals have always been balanced around having the great utility that the Druid class comes with, but I've never really seen any admission that Ferals have to work harder for that utility than any other spec/class. The only thing remotely similar had been Warrior stances, but the trend has been to make everything important usable in any stance as of late. Frequently, Bears just get stuck unable to take advantage of the group-saving abilities that other druid specs and other classes can access freely.