You specifically stated that Astrologian has never appeared before in ANY final fantasy game. You quantified it differently than I did my own statement. By stating that it had never appeared in ANY Final Fantasy game you permitted me to use the spin off games to prove you wrong. Even though I do not consider the spin off games part of the main series, that doesn't change the fact that they are STILL Final Fantasy Games and as such part of the Franchise. To make matters even more poignant, Final Fantasy Tactics takes place in the world of Ivalice, Ivalice is the same world that Final Fantasy XII takes place in. So technically speaking, Final Fantasy XII is a direct sequel to the Final Fantasy Tactics series, thus making Final Fantasy Tactics indirectly a part of the main series, despite being a spin-off.
It should be interesting to note that Final Fantasy Tactics (at least the first rendition) also has a Blue Mage in it.
I did not ask for the reason you would LIKE to see Blue in the game. I asked why you thought the game needed Blue in it. This means I want to know what you feel that adding Blue Mage to the game would actually add to the gaming experience that isn't already provided by one of the pre-existing classes. I am also curious which monster abilities specifically you think would make good Blue Magic spells... the only things I can think of are the various Area of Effect Attacks of several different non-Beastman or non-Human enemies (as the Beastman and Humans by and large use the same abilities and attacks as the currently existing classes).
I wasn't trying to break out the "I have better knowledge of FF History" card per se; its just that I have seen this topic come up several times over the years between this game and Final Fantasy XI (it only stopping in the latter's case when the class actually got added to the game), and I am getting ruddy tired of people insisting that this class "just needs to be added" with no real legitimate reasoning for why they feel that way.