Hey, MNK already gets "good defense skills and does {ridiculous} damage", so I say PLD should 'go for it'.
Inclusion of some 'Stances' along with reworking Cover, Shield Bash, etc would help balance this.

Perhaps such a stance would lend some of these 'rework' ideas? A Stance that augments Cover, shield Bash, Cure potency based off of enimity, etc. to maximize tanking. And then an opposite stance to augment Sword things, Divine Magic/flash?