also i seen alot of PLD go with (Damage -) instead of (Physical Damage -)? Is a reason behind that.
I don't think there are a lot of scenarios where you have to choose between these two. For JSE cape I usually do meva because DT is ludicrously easy to cap on other gear. DT covers physical, magical, and breath damage so it is better than PDT pound-for-pound. At the risk of getting into the weeds, there are a lot of important stats to consider in tanking sets.
Also most endgame content you would still be taking some what damage even with the above gear set. Just not as much compare to mages and DPS.
Depends greatly on the event. In Omen, for example, the vast majority of enemies will do 0 damage to you. This means that "Converts physical damage to MP" gear is basically worthless. If you're in Sortie, most of the trash will do 0 damage and the bosses do primarily magical damage.
Sometimes you will be taking above-0 damage (Sheol C perhaps) but realistically if you're taking 50 damage/hit, getting 4 MP back from the empy head is nice, but not really anything to write home about. 20 of those hits will cause you to get a single Cure IV. Compared to things like getting Refresh III or a Ballad it's a drop in the bucket. Also consider you have options like Chivalry and Devotion (depending on party setup).