Why Magicians Should Max Magic Guard

I tried to take on Capt. Latanica this afternoon on my own using a combination of SR (Shining Ray) and Summon Dragon which ended in a failure when my magic guard couldn't take the second hit of its "boat" attack due to my unmaxed Magic Guard:

My Priest's Magic Guard is only capped at Level 17 (71% of damage into MP, 29% into HP).
- My HP and MP are: 1520 & 7000 respectively.
- Cpt. Latanica's "boat" attack deals 3560 damage to me of which 1032 damage is reflected into my HP (1520) resulting in a "1 hit must heal" situation.
If my Magic Guard is maxed (80% of damage into MP, 20% into HP), the situation would be very different in this case:
- Taking that my HP and MP are: 1520 & 7000 respectively.
- Cpt. Latanica's "boat" attack deals 3560 damage to me of which 712 damage is reflected into my HP (1520) which means i can take 2 hits before having to heal or consume a potion.