AMZ is your party buff
i miss the old horn of winter
blood with abominations might
icy talons for frost
some kind of buff for unholy
DK should get the DH debuff , Give the monk debuff to warriors
That’s like saying that Power Word: Barrier is the Discipline Priest Party Buff or Power Infusion is the priest buff.
However, the actual priest buff is Power Word: Fortitude which firstly is BASELINE for all priests but has various talents that provide bonuses and benefits to this spell throughout the priests talent trees.
In each case for all of the various classes that have group buffs or beneficial utility debuffs etc. they are first and foremost BASELINE for the class. Then they have various talents throughout their talent trees that have some additional benefit or bonus that is applied to this ability to make it better in some way.
In the case of Warrior they have Battle Shout baseline but they also have the ability to choose the talent Rallying Cry which is VERY LOW in their Talent Tree (Tier 2) making it very accessible and easy to acquire with minimal impact on their choices further down the talent tree.
Taking your flawed logic that Anti Magic Zone is the Deathknight party buff means a fairly heavy investment in one track down the Deathknight Talent Tree to acquire that ability as it’s located on the 5th Tier of the tree. Even if they relocated the talent to be on the same tier as Rallying Cry to reduce the investment overhead for Deathknights in comparison you are still missing the fact that warriors actually have a group buff BASELINE and that additional talent is an optional bonus party buff they can elect to take as well.
The only way that AMZ could be considered to be the DK party buff would be if it was firstly BASELINE for all Deathknights with various talents placed in the Deathknight talent trees which provides additional benefits and changes to the ability.
Secondly I would also add to fit the PARTY BUFF CONCEPT it would need to be modified to be a buff which is placed on each member of the party/raid within a 40 yard radius like all of the other various class group buffs.
Alternatively and to be honest my personal preference would be for them to add a new baseline ability that provides each member of the Deathknights party/raid their own personal Anti Magic Shield. Then have various talents that provide additional benefits or bonuses to that baseline ability.
This gives Deathknights a very unique type of Party/Raid buff baseline that any group or raid will find advantageous in any part of the game.
Then AMZ becomes an optional additional choice that a Deathknight can take just like a warrior opting to take Rallying Cry.
Just my 2 cents