I posted it in a separate thread, but the idea of a tank inspired by the Judges in Final Fantasy could definitely work and to me is one of the current top concepts for a new tank, alongside or perhaps just behind Mystic Knight.
As others have pointed out, there are potential complications around trying to make it exactly what Judges have been in the Ivalice based FF games, but that's why I said "inspired" instead of "based on".

First off, just give them a different name than Judge but still carries the same general idea. Personally I like Arbiter.
A large 2-handed hammer could work as the weapon since people seem to really want that for a tank weapon, plus it's kind of like a giant gavel.
Give the abilities and weaponskills names based on legal jargon or referencing law and justice. Here are some random examples just off the top of my head: Gap Closer - Swift Justice, Combo pt.1 - Arraigning Blow, Combo pt.2 - Proceeding Strike, Combo pt.3 - Final Verdict.
Lorewise they can simply be champions that appear during times of great upheaval when evil ravages the land, taking up massive hammers to mete out justice to the guilty and defending the innocent. Further details that ties them into the history of the game-world can be done by the devs on the writing team.