DPS off-tank build isn't too useful outside of CT in my opinion. Most fights either only require one tank or tank swapping, so DPS build isn't too practical.

All the HM primals just require one tank. It might be viable for Garuda EX, but Titan and Ifrit EX need tank swapping and if you use STR items, you will be too squishy.

T1 might be viable until the Snake split, T2 and T4 it probably won't be viable since you have to tank swap / tank adds. T5 maybe, but snakes hits hard.

Will be extremely fun for CT though.