Lets see:
- solo ganking - beast mode, charge+quick escape proc and you catch any range/healer. Any melee should loose 1vs1 if such wp/dok knows what he is doing
- single target 100% uptime detaunt, great for 1vs2
- sc pugging - also great
Group play:
- dmg output comparable with melee classe
- medium armor, no mechanics requiring positional attacks or waiting for rage to go high taking half your armor and resists - full dmg from first hit
- heal in spammable attack
- high single target channel heal, allowing such "dps" to single target focused team member or himself if need to
- option to remove disarm - no melee class have it, allowing again to continue damaging and healing
- quickest cd on snare/root immunity than any other melee, effectively making them twice more mobile than real melees
- parry/crit tactic, most melees have no equivalent and effectively lower parry/crit than dok/wp can get
- auto attack 50% increase tactic, only few melees have it
- covenant/prayer effectively buffing team with 100% uptime
- ini debuff openers
- option to cleanse
- option to ressurect team members
- shatter enchantement
- dok - perma heal debuff
Id say its quite few advantages right here from top of my head.