If Holy Sheltron were DMG mit instead of block(or have an extra DMG mit CD)along with veil putting a shield on the caster, then PLD would be in a great spot defensively. That would allow them to kitchen sink CDs effectively like the other tanks can.

If it had the above changes AND be able to use HG twice per fight like WAR can, then it would probably be the best defensive tank (how it should be).