I think the leaks might have a bit to do with it, only that when the leak came out, we had no concept of a specialized combat job. Having a class with a very narrow focus and limited usability isn't new. Crafters and gatherers literally do one thing. They have content that's their one thing and they make/harvest stuff. In the barest bones concept, this limited job isn't new. However, before the Blue Mage fans eat me alive, I totally get you are sad and disappointed. I would have been the same way if my favorite class, RDM had been given this treatment.
So I get that you are upset and you have very right to be. But, if we hadn't had this leak saying we were absolutely getting Blue Mage, we would have heard it at the Keynote for the very first time. They were pretty upfront about the fact it wasn't a normal job. So, for the last however months since the leak, the community has thought it was just a normal job rather than a new type of job. This isn't saying that the disappointment wouldn't have been there had the leak not happened, but I do think the result wouldn't have been quite so bad, the expectations to hear about it wouldn't have been there. This leaker is actually pretty terrible, trying to take all surprise out of the game announcements.
That being said, I am in the small minority that most play alone, or with close family and friends, I think it's kinda of nice that they are trying to help people like me enjoy the content. I have social anxiety and I'm also an introvert so sometimes I want to get lost in this beautiful world and not have to deal with other people. I love this game, just as I love nearly every other Final Fantasy, and I play it because it's precisely that, a Final Fantasy. This is literally the only MMO I have ever played. When I first started and encountered bullies left and right, my one lament was, "this story and game is so wonderful, I wish it was single player." I've since then come to enjoy some content with other people, but try to understand that just because someone plays an MMO it doesn't mean they play it for the same reasons you do.