This sadly was the problem, the WoD team took a lazy approach by making it a talent that converted Protection spec into Gladiator spec instead of making it a fourth selectable spec like druids (which in fairness was a perfectly fine shortcut from their POV as artifacts weren't even an idea at this point). Then the Legion team took the lazy approach of just removing it instead of finishing the job properly and adding a fourth artifact.
Guess it will stand as a testament that no matter how cool something is or how well received it is, lazy devs can always **** on your cereal.
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Blood DPS Deathknights, Frost tank Deathknights, Unholy tank Deathknights. All removed from game in one patch, it really sucked.