What could make Tenacity more relevant is to make every mitigation scales of it. Parry, Block, even mitigation skills should all have a "potency" with the actual damage reduction being based off Tenacity and Defense/MDefense. On top of that, Tenacity could also increase healing received. And yes, completely avoid Tenacity should make tanks much more fragile than they are right now.

Also, Direct Hit should simply not exists and be fused with Crit. I don't see why we need two stats that "randomly increases damage".