How did I prove your point? Dancers are not Thieves or Ninjas. Warriors are not Beastmasters, Dark Knights, or Rangers. Each job, while having overlapping skills, have other skills that define them. They have more than just subtle differences to set them apart. Beast and Necro would be the same job, different damage source.

You cannot argue that since Dancer and Thief share daggers they are the same job. Dancers are front line healers. They can deal damage while healing other players and debuffing the mob. Thieves are front line hate control. They are able to change enmity levels for other players while dealing a consistent amount of damage.

Dancers and Ninjas are not the same as one, again, is a front line healer, while the other is an evasion tank. While it's true that Dancers can also tank, they do it via a different skill set. Ninjas evade damage and cast elemental (damage, not elemental type) magic and debuff mobs via Ninjitsu. Dancers tank by hopefully evading damage, and healing what damage they do take. They also debuff but it's via job abilities and not magic.

Warriors the jacks of all trades. They can fill in for all damage types, whereas a Dark Knight or Ranger (the two examples I used) excel in two different weapons that pertain to their job. Dark Knights have job abilities and spells to compliment their damage, making them a pure damage dealing melee job. Rangers excel in the use of ranged weapons, and have abilities to increase their damage, making them a pure damage dealing ranged job. Warriors have damaging dealing abilities, and damage mitigation abilities. They also have hate control abilities. They can do it all. All three jobs have abilities that separate themselves from each other. They're not clones.

I'm making supposed baseless assumptions because you're not even trying to prove your point that they'd be different from each other. Looking at the above text that I've typed, I've left plenty of words left in my mouth, and I have even more to defend my side. I'm not proving any of your points.

There are several jobs in the game that have overlapping abilities (WHM, RDM, BLM, and SCH especially), but each job has something that separates them from each other, each job has something unique that separates them from other jobs. Even Puppet Master is more than just a Monk with a pet. You still have not answered this question, what would Necromancer have that would separate them from Beast Masters, aside from a different type of damage source?