You are explaining what I already know, and are completly missing my point.
Besides, as you said, we already have Black Mage that have been stripped from its iconic use of elemental weaknesses. We don't need another one.
Which is why they decided to try and keep the iconic aspect of BLU. But that required it being put aside from the current roster, and it getting dedicated content, because FFXIV doesn't work with elemental weaknesses and all that stuff BLU is mostly about. Just take a look at a wiki list of all Blue Magic that was used in the franchise. Now try to count the number of skills which simply wouldn't work in FFXIV without heavy tweeking.
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Why not? Who are you to say that every playable job ever should be heavily tweeked to fit the mould? Who are you to kill the creativity of breaking rules and getting outside the usual mainstream content?
We've been asking for new and original content that breaks the usual formula for ages. That's exactly what we got. And now you want to get back into strictly respecting the formula? People never know what they want it seems.
Oh yeah, let me use Aqua Breath on a Water resistant enemy. Let me use Bad Breath on an enemy immune to status effects. Let me use Death Lv.5 on a level 42 enemy. Let my use Goblin Punch on an enemy not sharing my level. Let me use Magic hammer on an enemy without MP to steal. Let me use Level.? Holy on enemies not having a level which is a multiple of the last digit of how much gil I have...
Blue magic was always about weird situational skills that are very much conditionnal and should be used only in the right situation. All that while managing your MP in order not to burn it by only using the most powerful stuff you have.
Blue magic isn't about having a set rotation and a fixed number of skills. That'd be for a Boring Mage, not a Blue Mage. And we have a bunch of Boring Mages already.
That is what you do with blue magic. "Learning skills from monsters" is only a part of that gameplay. Ignoring the rest is a great disservice to that iconic job with its very special gameplay.
Maybe you would be okay with a butchered Blue Mage and Blue Magic. I wouldn't.