the way i see it:

Gld - 90% tank (Heavy Armor, Shield, Area threat skill, Most of the defensive skills availiable both from main class and shield offhand, Lots of HP)
Mrd - 70% tank (Heavy armor, front-cone basic attacks/threat skills, Intimidate, Still lots of HP)
Pug - 50% tank (Higher evasiveness, still lots of HP)
Lnc - 30% tank (only because they can wear defensive armor and can parry)
Arc - 10% tank (lighter armors, weapon cant parry, but also the highest damage of the DoW classes)

Lnc can only tank if it steals skills from the top 2 and has their R36 affinity skill, without doing that, it is DPS.

Gld + Mrd skills or Mrd + Gld skills = perfect tanks.