I don't think you can make any decisions about what the best gear to have in all situations is by running a PUG. For the sake of discussion, CC/AV should be done in 25mins or less, and even then running 20mins is pretty average for groups that know what they're doing. When we discuss "how to build a PLD", we should not be setting low standards for players and making that acceptable. If everyone did "just enough" to run raids in PUGs, then speed runs would be non-existent and bodies would never drop for that reason. Why set the bar low for your MMO's community by touting VIT/DEF builds being the best for end game raids? It isn't, not even close, and no one should be teaching new players that it is. I am glad a player stating that way can "hold their own" in a PUG, but the question is comes down to is "how long did it take?" Princess can be killed in 90-120s depending on your setups.
I could take a gear set for PLD and build a crappy party to go "test" it in a dungeon run. If efficiency is low, then it's low, and a tank should not be contributing to that if they can help it. Gimping yourself on purpose because you're headstrong about a build is not the way MMOs ought to be played by people who have goals for themselves.
On the way up in leveling, VIT/DEF isn't useful either. People run DPS builds for GLA/PLD because hate doesn't matter. When you get to end game, Enmity is #1 for gear choices. If someone here has full HDL and full DPS DL for PLD and wants to compare, go for it. I guarantee that against players worth their salt, HDL wins every time. I personally look at what is possible in a MMO. The upper echelon of the class is what should be aimed for at all times. Yes, "sacrifices" get made along to way (such as taking a little bit more damage on PLD), but when the rest of your party is working towards their strengths as well, everything just works better. Healers can keep a PLD with 3k HP alive just the same as a WAR with 4k when they know how to play their class.
tl;dr don't make yourself a victim of bad advice and roll with it because it looks like it works. Just as there is always a bigger fish, there is always a better way to gear yourself if you're not wearing best in slot.
Lastly: what is your gear setup that you can consider "stressing" him? Also, stripping out common aspects of battle does not give you a good indication of anything. As a DPS, you should be using attack food, bringing that gap up, and the tank has to be able to accommodate for that in real time. In other words, your test is not really accurate off the bat.