Honestly, the only time I ever felt the pinch of having only sword oath and no shield is if I was trying to tank 4+ targets against an AOE BLM and a 'pop everything on pull' BRD at the same time. And frankly, that sucks to deal with as a warrior too. Otherwise, even in sword, 2-3 flashes followed by cycling halone combos is generally enough to handle threat. Tank survival really doesn't start getting questionable until 40+ anyhow, with the sole exception of your first time stepping into Halatali at 20.