I think misunderstood something. Tenacity is not worse than parry in general, but worse in
physical defense.
I don't remember the exact numbers, so here an example:
If you've got x Tenacity, you get 5% mitigation.
If you've got x Parry, you get +50% parry rate - roughly about 10%
physical mitigation.
BUT, if we take into account that DRK lost its parry procs, Tenacity mitigates
every kind of damage, increases your
own healing on
yourself (I still don't know whether this is intentional or not) and on top of that, it increases your damage-output by roughly 3/4 of Determination's value - Tenacity becomes a way better stat than Parry.
(+1% damage for +217 Tenacity points or +167 Determination points. See this
list for reference!)
Tenacity is not bad by any means. It's just that DPS is meta, and you build your mitigation/heals around your maximised DPS, not vice versa.