The labels "Main Tank" and "Off Tank" used in their panel fundamentally are just names. What we consider a main tank or an off tank in actuality will likely differ anyhow.

Look at Evolved Paladin, the supposed "Main Tank" in that dichotomy. It still has Intervention (Holy Sheltron @ Ally), Divine Veil, Passage of Arms and Cover (Intervene @ Ally) - all the tools of why we consider Paladin to be a strong off-tank in the first place. Does this scream "this will never be used in an OT position" to you?

Likewise, you can make "Off Tanks" work as main tank. Those dichotomy labels are just that, labels - poorly picked ones that do not reflect position but rather functions of how mitigation may operate. Every tank will still have invulns and baseline mitigations (Rampart, 40%, Reprisal, likely a Short CD too).

Also, this is kinda whack to me considering how many see current Warrior as a de-facto Main Tank for the simple reasons like "this has the best sustain" and even just suggesting to play WAR in an OT position is seen as heresy. The only people enforcing MT and OT designation is us, the players.

You still wanna MT as WAR-DRK-GNB? You still wanna OT as PLD-newJob? Do it! It will most likely not even be bad at all.