A tank that doesn't wear fending armor and use tank stats is likely never going to happen in this game. Adding more types of gear into already polluted loot pools is something they will strongly resist doing. The same goes for having different roles share gear. There's a reason that out of 9 dps jobs none of them wear healer or tank gear.

Having a tank that's squishy and meant to completely avoid damage is something impossibly hard to balance in the first place, they already have a hard time balancing the existing tanks that are all very similar to each other.

Your idea is just continuously all over the place and simply isn't feasible in the reality of the situation.