No, it's double standard. The game sets three roles.
Tank, healer and DPS. There is no "melee DPS" role, just like there is no "disciple of magic" role. Those are categories WITHIN a role ("disciple of..." is a category across roles...).
"Melee/Ranged/Caster DPS" are a type of DPS. Not a role. Don't believe?!
Here. You can clearly see that they fall under a general role of DPS.
It's obvious that tanks and healers don't have such type distinction...seeing as they have only ONE type currently. I can assure you that as soon as they'll get at least two more of a different type (possibly even a single different class) they'll get divided just like this.
That's EXACTLY why yours is a double standard. You compare a sub-type of a role with a role and use that as argument that the ROLE to which that sub-type belongs to needs more new jobs than the ROLE that have a lot less jobs overall. If you don't understand that distinction...then it's a lost cause. You're just a DPS fanatic.