Ya know...you guys ought to check the recent interview on Reddit. Yoshida explicitly explains why BLU couldn't be in XIV at first.
https://www.reddit.com/r/ffxiv/comme...shida_summary/
Here's an excerpt from the interview that I believe is important, quoted from Yoshida himself:
"If we were to implement BLU as a normal job, there would be restrictions like "I can't raid until i learn all my new moves" or "I can't go to dungeons because i haven't learned those AoEs". You might think "I'm fine with that" at first, but you have to do that for every expansion. Everyone else is farming while you are learning to get to the startline, and it ends up being just annoying. Then what happens? The world fist teams won't use BLU. That doesn't mean we can just let BLUs have magic with extremely tilted synergies, because then BLU just becomes mandatory. If we are put in that situation where BLU has to be treated as a normal job, you won't be able to play BLU the way it's supposed to be fun."
This explanation tells us quite a bit about why BLU can't be brought into the raid scene. Let alone, there's more in the interview saying how difficult it could be to balance given it's a multi-purpose job. I'd recommend reading it so as to get an understanding as to Yoshida and the dev team's perspective on why they created a "limited job".