Warrior isn't squishy. Our tank stance doesn't reduce damage the way Shield Oath and Grit does, but we have more HP than they do, and when healers heal us, they heal us for more. In the end, it's balanced out. You don't need to worry about becoming "more tanky" via materia.

If you're worried about how squishy you might be, don't tank in Deliverance all the time, use your cooldowns properly, and learn when to best apply Inner Beast.

Now if you want to meld Determination because of damage, I'm not really sure yet. I'm currently running full crit and it's kinda disappointing how low my crit rate is. But maybe I just feel that way because we don't have Internal Release anymore. Still don't know if it's worth going Direct Hit though. I don't think it's worth trying until Savage comes out tomorrow, since there might be changes.