So, what is the hold up on Beastmaster?

[CKNovel]

So what? FF14 is a braindead easy game. So what if one pet does 2% more damage than another? PvE isn't competitive. And if pet balance really is a problem, just do what WoW did and allow you to stat swap pets so they all have the same level of competitiveness.

We're not talking about damage alone but mechanic as well.
What if we could capture a Morbol or Malboro and have it spew its 30 debuff on the ennemy?
Could you get the Mist dragon and freeze the ennemy?
What about the size of the ennemy? You'd have to be able to hide it or reduce its size.
What if an ennemy is able to heal, wouldn't it be broken?

You'd have to limit the possible capturable monster, then limit their utility and remove all flavor until all that remains is a cosmetic with stats.
You'll have to limit the job, for the same reason that Blue mage isn't playable in high end content.