I feel like you didn't even read my post. You simply saw my name and tried to argue against me without even understanding what I was saying. Because I already said that it wasn't about them being able to do it or not a way or another. Could have they came up with a concept for a regular job Blue Mage? Yes. They simply chose another route.
I have literally no idea why you went on about "they could have done it if they did this and that!". The theorical possibility of doing it is something I never argued against. (What I often argue against are the bad and flawed ideas and suggestions people throw on the table as if they were perfect. But that's another story.)
And I also conceeded that some of their justifications are indeed weak. No need to repeat to me what I already said.
You don't understand what kind of creative freedom for a low investment in balance does limited jobs provide? If you don't get what are the benefits of not having to make a job fit into the very narrow space that the current regular job balance requires, then you are literally asking me how are jobs balanced in this game and why is it restrictive to the point that it made Square Enix, the very creators of this game and the Final Fantasy franchise, felt that it was a good idea to take a different approach for one job that has been consistantly playing with weirdness and the boundaries of the game design space in previous titles.
And that's something I shouldn't have to explain to someone claiming to have a background in game design. Which is why I actually don't believe that you don't understand. I suspect that you are just so frustrated that you don't want to understand. Also -despite your claims regarding your experience- you act like ressources are infinite, and that they "could do it" without considering one second that investing in making Blue Mage "DF ready" is simply not something they determined to be worthwhile.
In short, "just make an entirely new set of skills balanced like all the other jobs so I can do my daily roulettes!" is something people often say lately, without understanding what would be necessary for it to happen.
I'm sorry that you don't understand the game design benefits of limited jobs. I'm also sorry that you don't understand the underlying consequences of what you are asking. Especially since you claimed to have a background in game design. And finally, I have to give you an apology. When I said that "anyone with a little bit of game design knowledge would be able to understand", it was implied that what was needed was a "little bit of good game design knowledge". Sorry if that wasn't clear enough.
Regardless, "I don't understand why they did that, so I'll simply say that they are lazy" is not the mark of a good game designer. At least, you never claimed to be one. That being said, if you think that you are, feel free to send them your resume.
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Tl;dr: Would it be nice if BLU was somehow DF and raid ready? Sure. But it's not, and the reasons why are obvious. Sorry if you don't understand them.