If a tank melded only Direct Hit on the ilvl450 Crafted gear, he could reach 2780 Direct Hit meaning he would gain 11.5% Damage increase ON PHYSICAL ATTACKS. But you would have to meld ONLY Direct Hit to reach that.
if a tank melded Tenacity as his primary stats on a ilvl450 Crafted gear, he could reach 3214 Tenacity meaning he would gain 9.7% Damage increase, 9.7% Damage Mitigation + 9.7% more self healing. That's just for Tenacity, that's not counting the other melds you have to put on the empty materia slots like Skillspeed and Crit/Det.
This is based after calculating using the 5.0 "Theorycrafted" job stat weights on this link.
https://www.reddit.com/r/ffxiv/comme...tat_intervals/
Pretty much a no brainer Tenacity > Direct Hit. Even SquareEnix knows Tank's don't need to stack Direct Hit by giving it the same base Direct Hit as a naked Botanist.