Despite SE's efforts tanks are still taking Strength accessories. By making STR and VIT equal in regards to attack power, secondary stats are the deciding factor.
Fending accessories are filled with parry and accuracy, both lackluster secondary stats.
Slaying accessories have the desired secondary stats that tanks want to increase their damage.
The only real way to solve this is one of two ways. Make parry worthwhile or make Strength lower than Vitality in terms of damage.