He's right. Don't stress too much over what you meld. The DPS difference between the worst possible melds and the best is less than 3%. Variations in player skill account for MUCH more than that, so work on getting your rotation down.
Personally, I like all Direct Hit for PLD right now, since they do not need skill speed for anything and det and crit are sub-optimal with the current tier of gear. This is expected to change later on once gear starts getting better. Crit typically pulls ahead once you are able to stack enough of it.
As far as Tenacity, players are largely in two groups:
Pro-Tenacity: Believes that the most important job of a tank is to be able to reduce as much incoming damage as possible, Tank DPS, while important, plays a less important role than defense. Plus, if you stack tenacity, then you can use the same gear sets for all 4 tanks pretty much, since all of the tanks benefit equally from Tenacity. The argument is commonly made that a higher tenacity stat reduces healing requirements a little, so healers can squeeze out a little more damage to offset what the tank loses.
Pro-DPS(crit, det, direct hit): Believes that in the current raid tier, DPS checks are the most difficult obstacle to overcome, so every tiny amount of DPS matters. The big argument made here is this: Encounter design is such that tanks are either dealing with a tank buster or auto attack damage. Auto attack damage is typically so low, that tenacity has a minimal effect on it anyways. Tank-busters are easily dealt with when properly mitigated by cooldowns, so it is a rare occurrence that the damage reduction from tenacity will ever make a significant difference. Plus, healing in the game is so powerful that it is common to overheal by 5-10% anyways, even when playing optimally, so tenacity doesn't really help healers much. The unfortunate downside to stacking these stats; however, is that all tanks don't benefit from them equally. WAR largely gets left out to dry right now because DH is the optimal stat for the other 3 tanks, but it is pretty bad on WAR due to how Inner Release and Infuriate work, so to be able to switch between all tanks requires you to remeld when you switch or to have a 2nd set of equipment.
I am in the Pro-DPS camp, but both arguments are valid and have their merits/detriments.