Complex sentence: While not "always" a disadvantage, this is a concern in PvP combat, plus a priest, mage, or paladin can just remove them, whilst a warlock cannot remove DOTs cast on itself ourside of a spellstone.
Split into simpler sentences: While not "always" a disadvantage, this is a concern in PvP combat. Plus, a priest, mage, or paladin can just remove them, whilst a warlock cannot remove DOTs cast on itself unless it's through the use of a spellstone.