if their mp is either half full or full, at any point in the dungeon while foes are present, that's also a red flag
i give it okay if it half full for DRK and PLD, sometimes tank just want the easy way out (just do aoe combo and thats that) and i admit i do that too when iam doing my dailies (in case of PLD i save some just in case of emergency heal), i mean the important aspect is the defensive CD for me at least.

but in boss fight i agree, if i see DRK or PLD mp is not empty 80% of the time during boss fight, thas bad. not the worst, but bad yeah.